  
  [1X5 [33X[0;0YAttributes and operations[133X[101X
  
  
  [1X5.1 [33X[0;0YVertices and edges[133X[101X
  
  [1X5.1-1 DigraphVertices[101X
  
  [33X[1;0Y[29X[2XDigraphVertices[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA list of positive integers.[133X
  
  [33X[0;0YReturns the vertices of the digraph [3Xdigraph[103X.[133X
  
  [33X[0;0YNote  that  the  vertices  of  a  digraph  are  always the range of positive
  integers  from  [10X1[110X  to the number of vertices of the graph, [2XDigraphNrVertices[102X
  ([14X5.1-2[114X).  Arbitrary [13Xlabels[113X can be assigned to the vertices of a digraph; see
  [2XDigraphVertexLabels[102X ([14X5.1-10[114X) for more information about this.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xgr := Digraph(["a", "b", "c"],[127X[104X
    [4X[25X>[125X [27X                 ["a", "b", "b"],[127X[104X
    [4X[25X>[125X [27X                 ["b", "c", "a"]);[127X[104X
    [4X[28X<immutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphVertices(gr);[127X[104X
    [4X[28X[ 1 .. 3 ][128X[104X
    [4X[25Xgap>[125X [27Xgr := Digraph([1, 2, 3, 4, 5, 7],[127X[104X
    [4X[25X>[125X [27X                 [1, 2, 2, 4, 4],[127X[104X
    [4X[25X>[125X [27X                 [2, 7, 5, 3, 7]);[127X[104X
    [4X[28X<immutable digraph with 6 vertices, 5 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphVertices(gr);[127X[104X
    [4X[28X[ 1 .. 6 ][128X[104X
    [4X[25Xgap>[125X [27XDigraphVertices(RandomDigraph(100));[127X[104X
    [4X[28X[ 1 .. 100 ][128X[104X
    [4X[25Xgap>[125X [27XD := CycleDigraph(IsMutableDigraph, 3);[127X[104X
    [4X[28X<mutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphVertices(D);[127X[104X
    [4X[28X[ 1 .. 3 ][128X[104X
  [4X[32X[104X
  
  [1X5.1-2 DigraphNrVertices[101X
  
  [33X[1;0Y[29X[2XDigraphNrVertices[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YAn non-negative integer.[133X
  
  [33X[0;0YReturns the number of vertices of the digraph [3Xdigraph[103X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xgr := Digraph(["a", "b", "c"],[127X[104X
    [4X[25X>[125X [27X                 ["a", "b", "b"],[127X[104X
    [4X[25X>[125X [27X                 ["b", "c", "a"]);[127X[104X
    [4X[28X<immutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphNrVertices(gr);[127X[104X
    [4X[28X3[128X[104X
    [4X[25Xgap>[125X [27Xgr := Digraph([1, 2, 3, 4, 5, 7],[127X[104X
    [4X[25X>[125X [27X                 [1, 2, 2, 4, 4],[127X[104X
    [4X[25X>[125X [27X                 [2, 7, 5, 3, 7]);[127X[104X
    [4X[28X<immutable digraph with 6 vertices, 5 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphNrVertices(gr);[127X[104X
    [4X[28X6[128X[104X
    [4X[25Xgap>[125X [27XDigraphNrVertices(RandomDigraph(100));[127X[104X
    [4X[28X100[128X[104X
    [4X[25Xgap>[125X [27XD := CycleDigraph(IsMutableDigraph, 3);[127X[104X
    [4X[28X<mutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphNrVertices(D);[127X[104X
    [4X[28X3[128X[104X
  [4X[32X[104X
  
  [1X5.1-3 DigraphEdges[101X
  
  [33X[1;0Y[29X[2XDigraphEdges[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA list of lists of two positive integers.[133X
  
  [33X[0;0YReturns a list of edges of the digraph [3Xdigraph[103X, where each edge is a pair of
  elements of [2XDigraphVertices[102X ([14X5.1-1[114X) of the form [10X[source,range][110X.[133X
  
  [33X[0;0YThe  entries  of [10XDigraphEdges([110X[3Xdigraph[103X[10X)[110X are in one-to-one correspondence with
  the  edges  of [3Xdigraph[103X. Hence [10XDigraphEdges([110X[3Xdigraph[103X[10X)[110X is duplicate-free if and
  only if [3Xdigraph[103X contains no multiple edges.[133X
  
  [33X[0;0YThe  entries  of  [10XDigraphEdges[110X  are  guaranteed  to be sorted by their first
  component  (i.e.  by  the source of each edge), but they are not necessarily
  then sorted by the second component.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xgr := DigraphFromDiSparse6String(".DaXbOe?EAM@G~");[127X[104X
    [4X[28X<immutable multidigraph with 5 vertices, 16 edges>[128X[104X
    [4X[25Xgap>[125X [27Xedges := ShallowCopy(DigraphEdges(gr));; Sort(edges);[127X[104X
    [4X[25Xgap>[125X [27Xedges;[127X[104X
    [4X[28X[ [ 1, 1 ], [ 1, 3 ], [ 1, 3 ], [ 1, 4 ], [ 1, 5 ], [ 2, 1 ], [128X[104X
    [4X[28X  [ 2, 2 ], [ 2, 3 ], [ 2, 5 ], [ 3, 2 ], [ 3, 4 ], [ 3, 5 ], [128X[104X
    [4X[28X  [ 4, 2 ], [ 4, 4 ], [ 4, 5 ], [ 5, 1 ] ][128X[104X
    [4X[25Xgap>[125X [27XD := CycleDigraph(IsMutableDigraph, 3);[127X[104X
    [4X[28X<mutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphEdges(D);[127X[104X
    [4X[28X[ [ 1, 2 ], [ 2, 3 ], [ 3, 1 ] ][128X[104X
  [4X[32X[104X
  
  [1X5.1-4 DigraphNrEdges[101X
  
  [33X[1;0Y[29X[2XDigraphNrEdges[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YAn integer.[133X
  
  [33X[0;0YReturns the number of edges of the digraph [3Xdigraph[103X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xgr := Digraph([[127X[104X
    [4X[25X>[125X [27X[1, 3, 4, 5], [1, 2, 3, 5], [2, 4, 5], [2, 4, 5], [1]]);;[127X[104X
    [4X[25Xgap>[125X [27XDigraphNrEdges(gr);[127X[104X
    [4X[28X15[128X[104X
    [4X[25Xgap>[125X [27Xgr := Digraph(["a", "b", "c"],[127X[104X
    [4X[25X>[125X [27X                 ["a", "b", "b"],[127X[104X
    [4X[25X>[125X [27X                 ["b", "a", "a"]);[127X[104X
    [4X[28X<immutable multidigraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphNrEdges(gr);[127X[104X
    [4X[28X3[128X[104X
    [4X[25Xgap>[125X [27XD := CycleDigraph(IsMutableDigraph, 3);[127X[104X
    [4X[28X<mutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphNrEdges(D);[127X[104X
    [4X[28X3[128X[104X
  [4X[32X[104X
  
  [1X5.1-5 DigraphNrLoops[101X
  
  [33X[1;0Y[29X[2XDigraphNrLoops[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YAn integer.[133X
  
  [33X[0;0YThis  function  returns  the  number  of  loops  of the digraph [3Xdigraph[103X. See
  [2XDigraphHasLoops[102X ([14X6.2-1[114X).[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[2, 3], [1, 4], [3, 3, 5], [], [2, 5]]);[127X[104X
    [4X[28X<immutable multidigraph with 5 vertices, 9 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphNrLoops(D);[127X[104X
    [4X[28X3[128X[104X
    [4X[25Xgap>[125X [27XD := EmptyDigraph(5);[127X[104X
    [4X[28X<immutable empty digraph with 5 vertices>[128X[104X
    [4X[25Xgap>[125X [27XDigraphNrLoops(D);[127X[104X
    [4X[28X0[128X[104X
    [4X[25Xgap>[125X [27XD := CompleteDigraph(5);[127X[104X
    [4X[28X<immutable complete digraph with 5 vertices>[128X[104X
    [4X[25Xgap>[125X [27XDigraphNrLoops(D);[127X[104X
    [4X[28X0[128X[104X
  [4X[32X[104X
  
  [1X5.1-6 DigraphSinks[101X
  
  [33X[1;0Y[29X[2XDigraphSinks[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA list of vertices.[133X
  
  [33X[0;0YThis  function returns a list of the sinks of the digraph [3Xdigraph[103X. A sink of
  a digraph is a vertex with out-degree zero. See [2XOutDegreeOfVertex[102X ([14X5.2-10[114X).[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xgr := Digraph([[3, 5, 2, 2], [3], [], [5, 2, 5, 3], []]);[127X[104X
    [4X[28X<immutable multidigraph with 5 vertices, 9 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphSinks(gr);[127X[104X
    [4X[28X[ 3, 5 ][128X[104X
    [4X[25Xgap>[125X [27XD := CycleDigraph(IsMutableDigraph, 3);[127X[104X
    [4X[28X<mutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphSinks(D);[127X[104X
    [4X[28X[  ][128X[104X
  [4X[32X[104X
  
  [1X5.1-7 DigraphSources[101X
  
  [33X[1;0Y[29X[2XDigraphSources[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA list of vertices.[133X
  
  [33X[0;0YThis  function  returns  an  immutable  list  of  the sources of the digraph
  [3Xdigraph[103X.  A  source  of  a  digraph  is  a  vertex  with in-degree zero. See
  [2XInDegreeOfVertex[102X ([14X5.2-12[114X).[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xgr := Digraph([[3, 5, 2, 2], [3], [], [5, 2, 5, 3], []]);[127X[104X
    [4X[28X<immutable multidigraph with 5 vertices, 9 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphSources(gr);[127X[104X
    [4X[28X[ 1, 4 ][128X[104X
    [4X[25Xgap>[125X [27XD := CycleDigraph(IsMutableDigraph, 3);[127X[104X
    [4X[28X<mutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphSources(D);[127X[104X
    [4X[28X[  ][128X[104X
  [4X[32X[104X
  
  [1X5.1-8 DigraphTopologicalSort[101X
  
  [33X[1;0Y[29X[2XDigraphTopologicalSort[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA list of positive integers, or [9Xfail[109X.[133X
  
  [33X[0;0YIf  [3Xdigraph[103X  is  a  digraph  whose  only  directed  cycles  are  loops, then
  [10XDigraphTopologicalSort[110X returns the vertices of [3Xdigraph[103X ordered so that every
  edge's  source appears no earlier in the list than its range. If the digraph
  [3Xdigraph[103X  contains  directed  cycles  of  length  greater  than  [22X1[122X, then this
  operation returns [9Xfail[109X.[133X
  
  [33X[0;0YSee Section [14X1.1-1[114X for the definition of a directed cycle, and the definition
  of a loop.[133X
  
  [33X[0;0YThe  method  used  for  this  attribute has complexity [22XO(m+n)[122X where [22Xm[122X is the
  number  of  edges  (counting  multiple  edges as one) and [22Xn[122X is the number of
  vertices in the digraph.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[127X[104X
    [4X[25X>[125X [27X[2, 3], [], [4, 6], [5], [], [7, 8, 9], [], [], []]);[127X[104X
    [4X[28X<immutable digraph with 9 vertices, 8 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphTopologicalSort(D);[127X[104X
    [4X[28X[ 2, 5, 4, 7, 8, 9, 6, 3, 1 ][128X[104X
    [4X[25Xgap>[125X [27XD := Digraph(IsMutableDigraph, [[2, 3], [3], [4], []]);[127X[104X
    [4X[28X<mutable digraph with 4 vertices, 4 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphTopologicalSort(D);[127X[104X
    [4X[28X[ 4, 3, 2, 1 ][128X[104X
  [4X[32X[104X
  
  [1X5.1-9 DigraphVertexLabel[101X
  
  [33X[1;0Y[29X[2XDigraphVertexLabel[102X( [3Xdigraph[103X, [3Xi[103X ) [32X operation[133X
  [33X[1;0Y[29X[2XSetDigraphVertexLabel[102X( [3Xdigraph[103X, [3Xi[103X, [3Xobj[103X ) [32X operation[133X
  
  [33X[0;0YIf  [3Xdigraph[103X  is a digraph, then the first operation returns the label of the
  vertex  [3Xi[103X. The second operation can be used to set the label of the vertex [3Xi[103X
  in [3Xdigraph[103X to the arbitrary [5XGAP[105X object [3Xobj[103X.[133X
  
  [33X[0;0YThe  label  of  a  vertex can be changed an arbitrary number of times. If no
  label has been set for the vertex [3Xi[103X, then the default value is [3Xi[103X.[133X
  
  [33X[0;0YIf   [3Xdigraph[103X   is   a  digraph  created  from  a  record  with  a  component
  [10XDigraphVertices[110X,  then  the  labels  of the vertices are set to the value of
  this component.[133X
  
  [33X[0;0YInduced  subdigraphs,  and  some  other operations which create new digraphs
  from old ones, inherit their labels from their parents.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := DigraphFromDigraph6String("&DHUEe_");[127X[104X
    [4X[28X<immutable digraph with 5 vertices, 11 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphVertexLabel(D, 3);[127X[104X
    [4X[28X3[128X[104X
    [4X[25Xgap>[125X [27XD := Digraph(["a", "b", "c"], [], []);[127X[104X
    [4X[28X<immutable empty digraph with 3 vertices>[128X[104X
    [4X[25Xgap>[125X [27XDigraphVertexLabel(D, 2);[127X[104X
    [4X[28X"b"[128X[104X
    [4X[25Xgap>[125X [27XSetDigraphVertexLabel(D, 2, "d");[127X[104X
    [4X[25Xgap>[125X [27XDigraphVertexLabel(D, 2);[127X[104X
    [4X[28X"d"[128X[104X
    [4X[25Xgap>[125X [27XD := InducedSubdigraph(D, [1, 2]);[127X[104X
    [4X[28X<immutable empty digraph with 2 vertices>[128X[104X
    [4X[25Xgap>[125X [27XDigraphVertexLabel(D, 2);[127X[104X
    [4X[28X"d"[128X[104X
    [4X[25Xgap>[125X [27XD := Digraph(IsMutableDigraph, ["e", "f", "g"], [], []);[127X[104X
    [4X[28X<mutable empty digraph with 3 vertices>[128X[104X
    [4X[25Xgap>[125X [27XDigraphVertexLabel(D, 1);[127X[104X
    [4X[28X"e"[128X[104X
    [4X[25Xgap>[125X [27XSetDigraphVertexLabel(D, 1, "h");[127X[104X
    [4X[25Xgap>[125X [27XDigraphVertexLabel(D, 1);[127X[104X
    [4X[28X"h"[128X[104X
    [4X[25Xgap>[125X [27XInducedSubdigraph(D, [1, 2]);[127X[104X
    [4X[28X<mutable empty digraph with 2 vertices>[128X[104X
    [4X[25Xgap>[125X [27XDigraphVertexLabel(D, 1);[127X[104X
    [4X[28X"h"[128X[104X
  [4X[32X[104X
  
  [1X5.1-10 DigraphVertexLabels[101X
  
  [33X[1;0Y[29X[2XDigraphVertexLabels[102X( [3Xdigraph[103X ) [32X operation[133X
  [33X[1;0Y[29X[2XSetDigraphVertexLabels[102X( [3Xdigraph[103X, [3Xlist[103X ) [32X operation[133X
  
  [33X[0;0YIf  [3Xdigraph[103X  is  a  digraph,  then [10XDigraphVertexLabels[110X returns a copy of the
  labels of the vertices in [3Xdigraph[103X. [10XSetDigraphVertexLabels[110X can be used to set
  the  labels  of the vertices in [3Xdigraph[103X to the list of arbitrary [5XGAP[105X objects
  [3Xlist[103X, which must be of the same length as the number of vertices of [3Xdigraph[103X.[133X
  
  [33X[0;0YIf  the  list [3Xlist[103X is immutable, then the vertex labels are set to a mutable
  copy of [3Xlist[103X. Otherwise, the labels are set to exactly [3Xlist[103X.[133X
  
  [33X[0;0YThe  label  of  a  vertex can be changed an arbitrary number of times. If no
  label has been set for the vertex [3Xi[103X, then the default value is [3Xi[103X.[133X
  
  [33X[0;0YIf   [3Xdigraph[103X   is   a  digraph  created  from  a  record  with  a  component
  [10XDigraphVertices[110X,  then  the  labels  of the vertices are set to the value of
  this  component.  As  in  the  above, if the component is immutable then the
  digraph's  vertex  labels  are  set  to  a  mutable copy of [10XDigraphVertices[110X.
  Otherwise, they are set to exactly [10XDigraphVertices[110X.[133X
  
  [33X[0;0YInduced subdigraphs, and other operations which create new digraphs from old
  ones, inherit their labels from their parents.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := DigraphFromDigraph6String("&DHUEe_");[127X[104X
    [4X[28X<immutable digraph with 5 vertices, 11 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphVertexLabels(D);[127X[104X
    [4X[28X[ 1 .. 5 ][128X[104X
    [4X[25Xgap>[125X [27XD := Digraph(["a", "b", "c"], [], []);[127X[104X
    [4X[28X<immutable empty digraph with 3 vertices>[128X[104X
    [4X[25Xgap>[125X [27XDigraphVertexLabels(D);[127X[104X
    [4X[28X[ "a", "b", "c" ][128X[104X
    [4X[25Xgap>[125X [27XSetDigraphVertexLabel(D, 2, "d");[127X[104X
    [4X[25Xgap>[125X [27XDigraphVertexLabels(D);[127X[104X
    [4X[28X[ "a", "d", "c" ][128X[104X
    [4X[25Xgap>[125X [27XD := InducedSubdigraph(D, [1, 3]);[127X[104X
    [4X[28X<immutable empty digraph with 2 vertices>[128X[104X
    [4X[25Xgap>[125X [27XDigraphVertexLabels(D);[127X[104X
    [4X[28X[ "a", "c" ][128X[104X
    [4X[25Xgap>[125X [27XD := Digraph(IsMutableDigraph, ["e", "f", "g"], [], []);[127X[104X
    [4X[28X<mutable empty digraph with 3 vertices>[128X[104X
    [4X[25Xgap>[125X [27XSetDigraphVertexLabels(D, ["h", "i", "j"]);[127X[104X
    [4X[25Xgap>[125X [27XDigraphVertexLabels(D);[127X[104X
    [4X[28X[ "h", "i", "j" ][128X[104X
    [4X[25Xgap>[125X [27XInducedSubdigraph(D, [1, 3]);[127X[104X
    [4X[28X<mutable empty digraph with 2 vertices>[128X[104X
    [4X[25Xgap>[125X [27XDigraphVertexLabels(D);[127X[104X
    [4X[28X[ "h", "j" ][128X[104X
  [4X[32X[104X
  
  [1X5.1-11 DigraphEdgeLabel[101X
  
  [33X[1;0Y[29X[2XDigraphEdgeLabel[102X( [3Xdigraph[103X, [3Xi[103X, [3Xj[103X ) [32X operation[133X
  [33X[1;0Y[29X[2XSetDigraphEdgeLabel[102X( [3Xdigraph[103X, [3Xi[103X, [3Xj[103X, [3Xobj[103X ) [32X operation[133X
  
  [33X[0;0YIf  [3Xdigraph[103X  is  a  digraph without multiple edges, then the first operation
  returns  the  label  of  the  edge  from  vertex  [3Xi[103X  to vertex [3Xj[103X. The second
  operation  can  be  used  to  set the label of the edge between vertex [3Xi[103X and
  vertex [3Xj[103X to the arbitrary [5XGAP[105X object [3Xobj[103X.[133X
  
  [33X[0;0YThe  label  of  an  edge  can be changed an arbitrary number of times. If no
  label has been set for the edge, then the default value is [3X1[103X.[133X
  
  [33X[0;0YInduced  subdigraphs,  and  some  other operations which create new digraphs
  from  old  ones,  inherit  their  edge  labels  from their parents. See also
  [2XDigraphEdgeLabels[102X ([14X5.1-12[114X).[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := DigraphFromDigraph6String("&DHUEe_");[127X[104X
    [4X[28X<immutable digraph with 5 vertices, 11 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphEdgeLabel(D, 3, 1);[127X[104X
    [4X[28X1[128X[104X
    [4X[25Xgap>[125X [27XSetDigraphEdgeLabel(D, 2, 5, [42]);[127X[104X
    [4X[25Xgap>[125X [27XDigraphEdgeLabel(D, 2, 5);[127X[104X
    [4X[28X[ 42 ][128X[104X
    [4X[25Xgap>[125X [27XD := InducedSubdigraph(D, [2, 5]);[127X[104X
    [4X[28X<immutable digraph with 2 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphEdgeLabel(D, 1, 2);[127X[104X
    [4X[28X[ 42 ][128X[104X
    [4X[25Xgap>[125X [27XD := ChainDigraph(IsMutableDigraph, 5);[127X[104X
    [4X[28X<mutable digraph with 5 vertices, 4 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphEdgeLabel(D, 2, 3);[127X[104X
    [4X[28X1[128X[104X
    [4X[25Xgap>[125X [27XSetDigraphEdgeLabel(D, 4, 5, [1729]);[127X[104X
    [4X[25Xgap>[125X [27XDigraphEdgeLabel(D, 4, 5);[127X[104X
    [4X[28X[ 1729 ][128X[104X
    [4X[25Xgap>[125X [27XInducedSubdigraph(D, [4, 5]);[127X[104X
    [4X[28X<mutable digraph with 2 vertices, 1 edge>[128X[104X
    [4X[25Xgap>[125X [27XDigraphEdgeLabel(D, 1, 2);[127X[104X
    [4X[28X[ 1729 ][128X[104X
  [4X[32X[104X
  
  [1X5.1-12 DigraphEdgeLabels[101X
  
  [33X[1;0Y[29X[2XDigraphEdgeLabels[102X( [3Xdigraph[103X ) [32X operation[133X
  [33X[1;0Y[29X[2XSetDigraphEdgeLabels[102X( [3Xdigraph[103X, [3Xlabels[103X ) [32X operation[133X
  [33X[1;0Y[29X[2XSetDigraphEdgeLabels[102X( [3Xdigraph[103X, [3Xfunc[103X ) [32X operation[133X
  
  [33X[0;0YIf  [3Xdigraph[103X  is  a  digraph  without  multiple edges, then [10XDigraphEdgeLabels[110X
  returns  a  copy  of  the  labels of the edges in [3Xdigraph[103X as a list of lists
  [10Xlabels[110X  such  that  [10Xlabels[i][j][110X  is  the label on the edge from vertex [10Xi[110X to
  vertex [10XOutNeighbours(digraph)[i][j][110X. [10XSetDigraphEdgeLabels[110X can be used to set
  the labels of the edges in [3Xdigraph[103X without multiple edges to the list [3Xlabels[103X
  of  lists  of arbitrary [5XGAP[105X objects such that [10Xlist[i][j][110X is the label on the
  edge from vertex [10Xi[110X to the vertex [10XOutNeighbours(digraph>[i][j][110X. Alternatively
  [10XSetDigraphEdgeLabels[110X  can  be  called  with binary function [3Xfunc[103X that as its
  second  argument that when passed two vertices [10Xi[110X and [10Xj[110X returns the label for
  the edge between vertex [10Xi[110X and vertex [10Xj[110X.[133X
  
  [33X[0;0YThe  label  of  an  edge  can be changed an arbitrary number of times. If no
  label has been set for an edge, then the default value is [10X1[110X.[133X
  
  [33X[0;0YInduced  subdigraphs,  and  some  other operations which create new digraphs
  from old ones, inherit their labels from their parents.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := DigraphFromDigraph6String("&DHUEe_");[127X[104X
    [4X[28X<immutable digraph with 5 vertices, 11 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphEdgeLabels(D);[127X[104X
    [4X[28X[ [ 1 ], [ 1, 1, 1 ], [ 1 ], [ 1, 1, 1 ], [ 1, 1, 1 ] ][128X[104X
    [4X[25Xgap>[125X [27XSetDigraphEdgeLabel(D, 2, 1, "d");[127X[104X
    [4X[25Xgap>[125X [27XDigraphEdgeLabels(D);[127X[104X
    [4X[28X[ [ 1 ], [ "d", 1, 1 ], [ 1 ], [ 1, 1, 1 ], [ 1, 1, 1 ] ][128X[104X
    [4X[25Xgap>[125X [27XD := InducedSubdigraph(D, [1, 2, 3]);[127X[104X
    [4X[28X<immutable digraph with 3 vertices, 4 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphEdgeLabels(D);[127X[104X
    [4X[28X[ [ 1 ], [ "d", 1 ], [ 1 ] ][128X[104X
    [4X[25Xgap>[125X [27XOutNeighbours(D);[127X[104X
    [4X[28X[ [ 3 ], [ 1, 3 ], [ 1 ] ][128X[104X
    [4X[25Xgap>[125X [27XD := CompleteBipartiteDigraph(IsMutableDigraph, 2, 3);[127X[104X
    [4X[28X<mutable digraph with 5 vertices, 12 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphEdgeLabels(D);[127X[104X
    [4X[28X[ [ 1, 1, 1 ], [ 1, 1, 1 ], [ 1, 1 ], [ 1, 1 ], [ 1, 1 ] ][128X[104X
    [4X[25Xgap>[125X [27XSetDigraphEdgeLabel(D, 2, 4, "a");[127X[104X
    [4X[25Xgap>[125X [27XDigraphEdgeLabels(D);[127X[104X
    [4X[28X[ [ 1, 1, 1 ], [ 1, "a", 1 ], [ 1, 1 ], [ 1, 1 ], [ 1, 1 ] ][128X[104X
    [4X[25Xgap>[125X [27XInducedSubdigraph(D, [1, 2, 3, 4]);[127X[104X
    [4X[28X<mutable digraph with 4 vertices, 8 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphEdgeLabels(D);[127X[104X
    [4X[28X[ [ 1, 1 ], [ 1, "a" ], [ 1, 1 ], [ 1, 1 ] ][128X[104X
    [4X[25Xgap>[125X [27XOutNeighbors(D);[127X[104X
    [4X[28X[ [ 3, 4 ], [ 3, 4 ], [ 1, 2 ], [ 1, 2 ] ][128X[104X
  [4X[32X[104X
  
  [1X5.1-13 DigraphInEdges[101X
  
  [33X[1;0Y[29X[2XDigraphInEdges[102X( [3Xdigraph[103X, [3Xvertex[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10YA list of edges.[133X
  
  [33X[0;0Y[10XDigraphInEdges[110X returns the list of all edges of [3Xdigraph[103X which have [3Xvertex[103X as
  their range.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[2, 2], [3, 3], [4, 4], [1, 1]]);[127X[104X
    [4X[28X<immutable multidigraph with 4 vertices, 8 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphInEdges(D, 2);[127X[104X
    [4X[28X[ [ 1, 2 ], [ 1, 2 ] ][128X[104X
  [4X[32X[104X
  
  [1X5.1-14 DigraphOutEdges[101X
  
  [33X[1;0Y[29X[2XDigraphOutEdges[102X( [3Xdigraph[103X, [3Xvertex[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10YA list of edges.[133X
  
  [33X[0;0Y[10XDigraphOutEdges[110X  returns  the list of all edges of [3Xdigraph[103X which have [3Xvertex[103X
  as their source.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[2, 2], [3, 3], [4, 4], [1, 1]]);[127X[104X
    [4X[28X<immutable multidigraph with 4 vertices, 8 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphOutEdges(D, 2);[127X[104X
    [4X[28X[ [ 2, 3 ], [ 2, 3 ] ][128X[104X
  [4X[32X[104X
  
  [1X5.1-15 IsDigraphEdge[101X
  
  [33X[1;0Y[29X[2XIsDigraphEdge[102X( [3Xdigraph[103X, [3Xlist[103X ) [32X operation[133X
  [33X[1;0Y[29X[2XIsDigraphEdge[102X( [3Xdigraph[103X, [3Xu[103X, [3Xv[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10Y[9Xtrue[109X or [9Xfalse[109X.[133X
  
  [33X[0;0YIn  the  first form, this function returns [9Xtrue[109X if and only if the list [3Xlist[103X
  specifies  an  edge  in  the  digraph  [3Xdigraph[103X. Specifically, this operation
  returns  [9Xtrue[109X  if  [3Xlist[103X  is a pair of positive integers where [3Xlist[103X[10X[1][110X is the
  source and [3Xlist[103X[10X[2][110X is the range of an edge in [3Xdigraph[103X, and [9Xfalse[109X otherwise.[133X
  
  [33X[0;0YThe  second  form  simply  returns [9Xtrue[109X if [10X[[3Xu[103X[10X, [3Xv[103X[10X][110X is an edge in [3Xdigraph[103X, and
  [9Xfalse[109X otherwise.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[2, 2], [6], [], [3], [], [1]]);[127X[104X
    [4X[28X<immutable multidigraph with 6 vertices, 5 edges>[128X[104X
    [4X[25Xgap>[125X [27XIsDigraphEdge(D, [1, 1]);[127X[104X
    [4X[28Xfalse[128X[104X
    [4X[25Xgap>[125X [27XIsDigraphEdge(D, [1, 2]);[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27XIsDigraphEdge(D, [1, 8]);[127X[104X
    [4X[28Xfalse[128X[104X
  [4X[32X[104X
  
  [1X5.1-16 IsMatching[101X
  
  [33X[1;0Y[29X[2XIsMatching[102X( [3Xdigraph[103X, [3Xlist[103X ) [32X operation[133X
  [33X[1;0Y[29X[2XIsMaximalMatching[102X( [3Xdigraph[103X, [3Xlist[103X ) [32X operation[133X
  [33X[1;0Y[29X[2XIsMaximumMatching[102X( [3Xdigraph[103X, [3Xlist[103X ) [32X operation[133X
  [33X[1;0Y[29X[2XIsPerfectMatching[102X( [3Xdigraph[103X, [3Xlist[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10Y[9Xtrue[109X or [9Xfalse[109X.[133X
  
  [33X[0;0YIf  [3Xdigraph[103X is a digraph and [3Xlist[103X is a list of pairs of vertices of [3Xdigraph[103X,
  then [10XIsMatching[110X returns [9Xtrue[109X if [3Xlist[103X is a matching of [3Xdigraph[103X. The operation
  [10XIsMaximalMatching[110X   returns   [9Xtrue[109X   if   [3Xlist[103X   is   a   maximal  matching,
  [10XIsMaximumMatching[110X   returns   [9Xtrue[109X   if  [3Xlist[103X  is  a  maximum  matching  and
  [10XIsPerfectMatching[110X  returns  [9Xtrue[109X  if [3Xlist[103X is a perfect, matching of [3Xdigraph[103X,
  respectively. Otherwise, each of these operations return [9Xfalse[109X.[133X
  
  [33X[0;0YA  [13Xmatching[113X [10XM[110X of a digraph [3Xdigraph[103X is a subset of the edges of [3Xdigraph[103X, i.e.
  [10XDigraphEdges([3Xdigraph[103X[10X)[110X, such that no pair of distinct edges in [10XM[110X are incident
  to  the  same vertex of [3Xdigraph[103X. Note that this definition allows a matching
  to  contain loops. See [2XDigraphHasLoops[102X ([14X6.2-1[114X). The matching [10XM[110X is [13Xmaximal[113X if
  it  is  contained in no larger matching of the digraph, is [13Xmaximum[113X if it has
  the  greatest cardinality among all matchings and is [13Xperfect[113X if every vertex
  of  the  digraph  is  incident  to an edge in the matching. Every maximum or
  perfect  matching is maximal. Note, however, that not every perfect matching
  of digraphs with loops is maximum.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[1, 2], [1, 2], [2, 3, 4], [3, 5], [1]]);[127X[104X
    [4X[28X<immutable digraph with 5 vertices, 10 edges>[128X[104X
    [4X[25Xgap>[125X [27XIsMatching(D, [[2, 1], [3, 2]]);[127X[104X
    [4X[28Xfalse[128X[104X
    [4X[25Xgap>[125X [27Xedges := [[3, 2]];;[127X[104X
    [4X[25Xgap>[125X [27XIsMatching(D, edges);[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27XIsMaximalMatching(D, edges);[127X[104X
    [4X[28Xfalse[128X[104X
    [4X[25Xgap>[125X [27Xedges := [[2, 1], [3, 4]];;[127X[104X
    [4X[25Xgap>[125X [27XIsMaximalMatching(D, edges);[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27XIsPerfectMatching(D, edges);[127X[104X
    [4X[28Xfalse[128X[104X
    [4X[25Xgap>[125X [27Xedges := [[1, 2], [3, 3], [4, 5]];;[127X[104X
    [4X[25Xgap>[125X [27XIsPerfectMatching(D, edges);[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27XIsMaximumMatching(D, edges);[127X[104X
    [4X[28Xfalse[128X[104X
    [4X[25Xgap>[125X [27Xedges := [[1, 1], [2, 2], [3, 3], [4, 5]];;[127X[104X
    [4X[25Xgap>[125X [27XIsMaximumMatching(D, edges);[127X[104X
    [4X[28Xtrue[128X[104X
  [4X[32X[104X
  
  [1X5.1-17 DigraphMaximalMatching[101X
  
  [33X[1;0Y[29X[2XDigraphMaximalMatching[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA list of pairs of vertices.[133X
  
  [33X[0;0YThis function returns a maximal matching of the digraph [3Xdigraph[103X.[133X
  
  [33X[0;0YFor the definition of a maximal matching, see [2XIsMaximalMatching[102X ([14X5.1-16[114X).[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := DigraphFromDiSparse6String(".IeAoXCJU@|SHAe?d");[127X[104X
    [4X[28X<immutable digraph with 10 vertices, 13 edges>[128X[104X
    [4X[25Xgap>[125X [27XM := DigraphMaximalMatching(D);; IsMaximalMatching(D, M);[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27XD := RandomDigraph(100);;[127X[104X
    [4X[25Xgap>[125X [27XIsMaximalMatching(D, DigraphMaximalMatching(D));[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27XD := GeneralisedPetersenGraph(IsMutableDigraph, 9, 2);[127X[104X
    [4X[28X<mutable digraph with 18 vertices, 54 edges>[128X[104X
    [4X[25Xgap>[125X [27XIsMaximalMatching(D, DigraphMaximalMatching(D));[127X[104X
    [4X[28Xtrue[128X[104X
  [4X[32X[104X
  
  [1X5.1-18 DigraphMaximumMatching[101X
  
  [33X[1;0Y[29X[2XDigraphMaximumMatching[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA list of pairs of vertices.[133X
  
  [33X[0;0YThis function returns a maximum matching of the digraph [3Xdigraph[103X.[133X
  
  [33X[0;0YFor the definition of a maximum matching, see [2XIsMaximumMatching[102X ([14X5.1-16[114X). If
  [3Xdigraph[103X  is  bipartite  (see [2XIsBipartiteDigraph[102X ([14X6.2-3[114X)), then the algorithm
  used   has   complexity  [10XO(m*sqrt(n))[110X.  Otherwise  for  general  graphs  the
  complexity  is  [10XO(m*n*log(n))[110X. Here [10Xn[110X is the number of vertices and [10Xm[110X is the
  number of edges.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := DigraphFromDigraph6String("&I@EA_A?AdDp[_c??OO");[127X[104X
    [4X[28X<immutable digraph with 10 vertices, 23 edges>[128X[104X
    [4X[25Xgap>[125X [27XM := DigraphMaximumMatching(D);; IsMaximalMatching(D, M);[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27XLength(M);[127X[104X
    [4X[28X5[128X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[5, 6, 7, 8], [6, 7, 8], [7, 8], [8], [127X[104X
    [4X[25X>[125X [27X                 [], [], [], []]);;[127X[104X
    [4X[25Xgap>[125X [27XM := DigraphMaximumMatching(D);[127X[104X
    [4X[28X[ [ 1, 5 ], [ 2, 6 ], [ 3, 7 ], [ 4, 8 ] ][128X[104X
    [4X[25Xgap>[125X [27XD := GeneralisedPetersenGraph(IsMutableDigraph, 9, 2);[127X[104X
    [4X[28X<mutable digraph with 18 vertices, 54 edges>[128X[104X
    [4X[25Xgap>[125X [27XM := DigraphMaximumMatching(D);;[127X[104X
    [4X[25Xgap>[125X [27XIsMaximalMatching(D, M);[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27XLength(M);[127X[104X
    [4X[28X9[128X[104X
  [4X[32X[104X
  
  
  [1X5.2 [33X[0;0YNeighbours and degree[133X[101X
  
  [1X5.2-1 AdjacencyMatrix[101X
  
  [33X[1;0Y[29X[2XAdjacencyMatrix[102X( [3Xdigraph[103X ) [32X attribute[133X
  [33X[1;0Y[29X[2XAdjacencyMatrixMutableCopy[102X( [3Xdigraph[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10YA square matrix of non-negative integers.[133X
  
  [33X[0;0YThis  function  returns the adjacency matrix [10Xmat[110X of the digraph [3Xdigraph[103X. The
  value  of  the matrix entry [10Xmat[i][j][110X is the number of edges in [3Xdigraph[103X with
  source  [10Xi[110X  and  range  [10Xj[110X. If [3Xdigraph[103X has no vertices, then the empty list is
  returned.[133X
  
  [33X[0;0YThe function [10XAdjacencyMatrix[110X returns an immutable list of lists, whereas the
  function  [10XAdjacencyMatrixMutableCopy[110X  returns a copy of [10XAdjacencyMatrix[110X that
  is a mutable list of mutable lists.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xgr := Digraph([[127X[104X
    [4X[25X>[125X [27X[2, 2, 2], [1, 3, 6, 8, 9, 10], [4, 6, 8],[127X[104X
    [4X[25X>[125X [27X[1, 2, 3, 9], [3, 3], [3, 5, 6, 10], [1, 2, 7],[127X[104X
    [4X[25X>[125X [27X[1, 2, 3, 10, 5, 6, 10], [1, 3, 4, 5, 8, 10],[127X[104X
    [4X[25X>[125X [27X[2, 3, 4, 6, 7, 10]]);[127X[104X
    [4X[28X<immutable multidigraph with 10 vertices, 44 edges>[128X[104X
    [4X[25Xgap>[125X [27Xmat := AdjacencyMatrix(gr);;[127X[104X
    [4X[25Xgap>[125X [27XDisplay(mat);[127X[104X
    [4X[28X[ [  0,  3,  0,  0,  0,  0,  0,  0,  0,  0 ],[128X[104X
    [4X[28X  [  1,  0,  1,  0,  0,  1,  0,  1,  1,  1 ],[128X[104X
    [4X[28X  [  0,  0,  0,  1,  0,  1,  0,  1,  0,  0 ],[128X[104X
    [4X[28X  [  1,  1,  1,  0,  0,  0,  0,  0,  1,  0 ],[128X[104X
    [4X[28X  [  0,  0,  2,  0,  0,  0,  0,  0,  0,  0 ],[128X[104X
    [4X[28X  [  0,  0,  1,  0,  1,  1,  0,  0,  0,  1 ],[128X[104X
    [4X[28X  [  1,  1,  0,  0,  0,  0,  1,  0,  0,  0 ],[128X[104X
    [4X[28X  [  1,  1,  1,  0,  1,  1,  0,  0,  0,  2 ],[128X[104X
    [4X[28X  [  1,  0,  1,  1,  1,  0,  0,  1,  0,  1 ],[128X[104X
    [4X[28X  [  0,  1,  1,  1,  0,  1,  1,  0,  0,  1 ] ][128X[104X
    [4X[25Xgap>[125X [27XD := CycleDigraph(IsMutableDigraph, 3);[127X[104X
    [4X[28X<mutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XDisplay(AdjacencyMatrix(D));[127X[104X
    [4X[28X[ [  0,  1,  0 ],[128X[104X
    [4X[28X  [  0,  0,  1 ],[128X[104X
    [4X[28X  [  1,  0,  0 ] ][128X[104X
  [4X[32X[104X
  
  [1X5.2-2 CharacteristicPolynomial[101X
  
  [33X[1;0Y[29X[2XCharacteristicPolynomial[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA polynomial with integer coefficients.[133X
  
  [33X[0;0YThis  function returns the characteristic polynomial of the digraph [3Xdigraph[103X.
  That  is it returns the characteristic polynomial of the adjacency matrix of
  the digraph [3Xdigraph[103X[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[127X[104X
    [4X[25X>[125X [27X[2, 2, 2], [1, 3, 6, 8, 9, 10], [4, 6, 8],[127X[104X
    [4X[25X>[125X [27X[1, 2, 3, 9], [3, 3], [3, 5, 6, 10], [1, 2, 7],[127X[104X
    [4X[25X>[125X [27X[1, 2, 3, 10, 5, 6, 10], [1, 3, 4, 5, 8, 10],[127X[104X
    [4X[25X>[125X [27X[2, 3, 4, 6, 7, 10]]);[127X[104X
    [4X[28X<immutable multidigraph with 10 vertices, 44 edges>[128X[104X
    [4X[25Xgap>[125X [27XCharacteristicPolynomial(D);[127X[104X
    [4X[28Xx_1^10-3*x_1^9-7*x_1^8-x_1^7+14*x_1^6+x_1^5-26*x_1^4+51*x_1^3-10*x_1^2\[128X[104X
    [4X[28X+18*x_1-30[128X[104X
    [4X[25Xgap>[125X [27XD := CompleteDigraph(5);[127X[104X
    [4X[28X<immutable complete digraph with 5 vertices>[128X[104X
    [4X[25Xgap>[125X [27XCharacteristicPolynomial(D);[127X[104X
    [4X[28Xx_1^5-10*x_1^3-20*x_1^2-15*x_1-4[128X[104X
    [4X[25Xgap>[125X [27XD := CycleDigraph(IsMutableDigraph, 3);[127X[104X
    [4X[28X<mutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XCharacteristicPolynomial(D);[127X[104X
    [4X[28Xx_1^3-1[128X[104X
  [4X[32X[104X
  
  [1X5.2-3 BooleanAdjacencyMatrix[101X
  
  [33X[1;0Y[29X[2XBooleanAdjacencyMatrix[102X( [3Xdigraph[103X ) [32X attribute[133X
  [33X[1;0Y[29X[2XBooleanAdjacencyMatrixMutableCopy[102X( [3Xdigraph[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10YA square matrix of booleans.[133X
  
  [33X[0;0YIf  [3Xdigraph[103X  is  a  digraph  with  a  positive  number  of  vertices [10Xn[110X, then
  [10XBooleanAdjacencyMatrix([110X[3Xdigraph[103X[10X)[110X  returns the boolean adjacency matrix [10Xmat[110X of
  [3Xdigraph[103X.  The  value  of  the  matrix entry [10Xmat[j][i][110X is [9Xtrue[109X if and only if
  there exists an edge in [3Xdigraph[103X with source [10Xj[110X and range [10Xi[110X. If [3Xdigraph[103X has no
  vertices, then the empty list is returned.[133X
  
  [33X[0;0YNote  that  the  boolean  adjacency  matrix loses information about multiple
  edges.[133X
  
  [33X[0;0YThe  attribute [10XBooleanAdjacencyMatrix[110X returns an immutable list of immutable
  lists, whereas the function [10XBooleanAdjacencyMatrixMutableCopy[110X returns a copy
  of the [10XBooleanAdjacencyMatrix[110X that is a mutable list of mutable lists.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xgr := Digraph([[3, 4], [2, 3], [1, 2, 4], [4]]);[127X[104X
    [4X[28X<immutable digraph with 4 vertices, 8 edges>[128X[104X
    [4X[25Xgap>[125X [27XPrintArray(BooleanAdjacencyMatrix(gr));[127X[104X
    [4X[28X[ [  false,  false,   true,   true ],[128X[104X
    [4X[28X  [  false,   true,   true,  false ],[128X[104X
    [4X[28X  [   true,   true,  false,   true ],[128X[104X
    [4X[28X  [  false,  false,  false,   true ] ][128X[104X
    [4X[25Xgap>[125X [27Xgr := CycleDigraph(4);;[127X[104X
    [4X[25Xgap>[125X [27XPrintArray(BooleanAdjacencyMatrix(gr));[127X[104X
    [4X[28X[ [  false,   true,  false,  false ],[128X[104X
    [4X[28X  [  false,  false,   true,  false ],[128X[104X
    [4X[28X  [  false,  false,  false,   true ],[128X[104X
    [4X[28X  [   true,  false,  false,  false ] ][128X[104X
    [4X[25Xgap>[125X [27XBooleanAdjacencyMatrix(EmptyDigraph(0));[127X[104X
    [4X[28X[  ][128X[104X
    [4X[25Xgap>[125X [27XD := CycleDigraph(IsMutableDigraph, 3);[127X[104X
    [4X[28X<mutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XPrintArray(BooleanAdjacencyMatrix(D));[127X[104X
    [4X[28X[ [  false,   true,  false ],[128X[104X
    [4X[28X  [  false,  false,   true ],[128X[104X
    [4X[28X  [   true,  false,  false ] ][128X[104X
  [4X[32X[104X
  
  [1X5.2-4 DigraphAdjacencyFunction[101X
  
  [33X[1;0Y[29X[2XDigraphAdjacencyFunction[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA function.[133X
  
  [33X[0;0YIf  [3Xdigraph[103X  is  a digraph, then [10XDigraphAdjacencyFunction[110X returns a function
  which  takes two integer parameters [10Xx, y[110X and returns [9Xtrue[109X if there exists an
  edge from vertex [10Xx[110X to vertex [10Xy[110X in [3Xdigraph[103X and [9Xfalse[109X if not.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xdigraph := Digraph([[1, 2], [3], []]);[127X[104X
    [4X[28X<immutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27Xfoo := DigraphAdjacencyFunction(digraph);[127X[104X
    [4X[28Xfunction( u, v ) ... end[128X[104X
    [4X[25Xgap>[125X [27Xfoo(1, 1);[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27Xfoo(1, 2);[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27Xfoo(1, 3);[127X[104X
    [4X[28Xfalse[128X[104X
    [4X[25Xgap>[125X [27Xfoo(3, 1);[127X[104X
    [4X[28Xfalse[128X[104X
    [4X[25Xgap>[125X [27Xgr := Digraph(["a", "b", "c"],[127X[104X
    [4X[25X>[125X [27X                 ["a", "b", "b"],[127X[104X
    [4X[25X>[125X [27X                 ["b", "a", "a"]);[127X[104X
    [4X[28X<immutable multidigraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27Xfoo := DigraphAdjacencyFunction(gr);[127X[104X
    [4X[28Xfunction( u, v ) ... end[128X[104X
    [4X[25Xgap>[125X [27Xfoo(1, 2);[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27Xfoo(3, 2);[127X[104X
    [4X[28Xfalse[128X[104X
    [4X[25Xgap>[125X [27Xfoo(3, 1);[127X[104X
    [4X[28Xfalse[128X[104X
    [4X[25Xgap>[125X [27XD := CycleDigraph(IsMutableDigraph, 3);[127X[104X
    [4X[28X<mutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27Xfoo := DigraphAdjacencyFunction(D);[127X[104X
    [4X[28Xfunction( u, v ) ... end[128X[104X
    [4X[25Xgap>[125X [27Xfoo(1, 2);[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27Xfoo(2, 1);[127X[104X
    [4X[28Xfalse[128X[104X
  [4X[32X[104X
  
  [1X5.2-5 DigraphRange[101X
  
  [33X[1;0Y[29X[2XDigraphRange[102X( [3Xdigraph[103X ) [32X attribute[133X
  [33X[1;0Y[29X[2XDigraphSource[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA list of positive integers.[133X
  
  [33X[0;0Y[10XDigraphRange[110X  and  [10XDigraphSource[110X  return the range and source of the digraph
  [3Xdigraph[103X.   More   precisely,   position   [10Xi[110X  in  [10XDigraphSource([3Xdigraph[103X[10X)[110X  and
  [10XDigraphRange([3Xdigraph[103X[10X)[110X  give,  respectively,  the source and range of the [10Xi[110Xth
  edge of [3Xdigraph[103X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xgr := Digraph([[127X[104X
    [4X[25X>[125X [27X[2, 1, 3, 5], [1, 3, 4], [2, 3], [2], [1, 2, 3, 4]]);[127X[104X
    [4X[28X<immutable digraph with 5 vertices, 14 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphSource(gr);[127X[104X
    [4X[28X[ 1, 1, 1, 1, 2, 2, 2, 3, 3, 4, 5, 5, 5, 5 ][128X[104X
    [4X[25Xgap>[125X [27XDigraphRange(gr);[127X[104X
    [4X[28X[ 2, 1, 3, 5, 1, 3, 4, 2, 3, 2, 1, 2, 3, 4 ][128X[104X
    [4X[25Xgap>[125X [27XDigraphEdges(gr);[127X[104X
    [4X[28X[ [ 1, 2 ], [ 1, 1 ], [ 1, 3 ], [ 1, 5 ], [ 2, 1 ], [ 2, 3 ], [128X[104X
    [4X[28X  [ 2, 4 ], [ 3, 2 ], [ 3, 3 ], [ 4, 2 ], [ 5, 1 ], [ 5, 2 ], [128X[104X
    [4X[28X  [ 5, 3 ], [ 5, 4 ] ][128X[104X
    [4X[25Xgap>[125X [27XD := CycleDigraph(IsMutableDigraph, 3);[127X[104X
    [4X[28X<mutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphRange(D);[127X[104X
    [4X[28X[ 2, 3, 1 ][128X[104X
    [4X[25Xgap>[125X [27XDigraphSource(D);[127X[104X
    [4X[28X[ 1, 2, 3 ][128X[104X
  [4X[32X[104X
  
  [1X5.2-6 OutNeighbours[101X
  
  [33X[1;0Y[29X[2XOutNeighbours[102X( [3Xdigraph[103X ) [32X attribute[133X
  [33X[1;0Y[29X[2XOutNeighbors[102X( [3Xdigraph[103X ) [32X attribute[133X
  [33X[1;0Y[29X[2XOutNeighboursMutableCopy[102X( [3Xdigraph[103X ) [32X operation[133X
  [33X[1;0Y[29X[2XOutNeighborsMutableCopy[102X( [3Xdigraph[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10YThe adjacencies of a digraph.[133X
  
  [33X[0;0Y[10XOutNeighbours[110X  returns  the list [10Xout[110X of out-neighbours of each vertex of the
  digraph  [3Xdigraph[103X.  More specifically, a vertex [10Xj[110X appears in [10Xout[i][110X each time
  there exists the edge [10X[i, j][110X in [3Xdigraph[103X.[133X
  
  [33X[0;0YThe  function  [10XOutNeighbours[110X returns an immutable list of lists, whereas the
  function [10XOutNeighboursMutableCopy[110X returns a copy of [10XOutNeighbours[110X which is a
  mutable list of mutable lists.[133X
  
  [33X[0;0YNote  that  the  entries  of  [10Xout[110X  are  not  guaranteed  to be sorted in any
  particular order.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xgr := Digraph(["a", "b", "c"],[127X[104X
    [4X[25X>[125X [27X                 ["a", "b", "b"],[127X[104X
    [4X[25X>[125X [27X                 ["b", "a", "c"]);[127X[104X
    [4X[28X<immutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XOutNeighbours(gr);[127X[104X
    [4X[28X[ [ 2 ], [ 1, 3 ], [  ] ][128X[104X
    [4X[25Xgap>[125X [27Xgr := Digraph([[1, 2, 3], [2, 1], [3]]);[127X[104X
    [4X[28X<immutable digraph with 3 vertices, 6 edges>[128X[104X
    [4X[25Xgap>[125X [27XOutNeighbours(gr);[127X[104X
    [4X[28X[ [ 1, 2, 3 ], [ 2, 1 ], [ 3 ] ][128X[104X
    [4X[25Xgap>[125X [27Xgr := DigraphByAdjacencyMatrix([[127X[104X
    [4X[25X>[125X [27X [1, 2, 1],[127X[104X
    [4X[25X>[125X [27X [1, 1, 0],[127X[104X
    [4X[25X>[125X [27X [0, 0, 1]]);[127X[104X
    [4X[28X<immutable multidigraph with 3 vertices, 7 edges>[128X[104X
    [4X[25Xgap>[125X [27XOutNeighbours(gr);[127X[104X
    [4X[28X[ [ 1, 2, 2, 3 ], [ 1, 2 ], [ 3 ] ][128X[104X
    [4X[25Xgap>[125X [27XOutNeighboursMutableCopy(gr);[127X[104X
    [4X[28X[ [ 1, 2, 2, 3 ], [ 1, 2 ], [ 3 ] ][128X[104X
    [4X[25Xgap>[125X [27XD := CycleDigraph(IsMutableDigraph, 3);[127X[104X
    [4X[28X<mutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XOutNeighbours(D);[127X[104X
    [4X[28X[ [ 2 ], [ 3 ], [ 1 ] ][128X[104X
  [4X[32X[104X
  
  [1X5.2-7 InNeighbours[101X
  
  [33X[1;0Y[29X[2XInNeighbours[102X( [3Xdigraph[103X ) [32X attribute[133X
  [33X[1;0Y[29X[2XInNeighbors[102X( [3Xdigraph[103X ) [32X attribute[133X
  [33X[1;0Y[29X[2XInNeighboursMutableCopy[102X( [3Xdigraph[103X ) [32X operation[133X
  [33X[1;0Y[29X[2XInNeighborsMutableCopy[102X( [3Xdigraph[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10YA list of lists of vertices.[133X
  
  [33X[0;0Y[10XInNeighbours[110X  returns  the  list  [10Xinn[110X of in-neighbours of each vertex of the
  digraph  [3Xdigraph[103X.  More specifically, a vertex [10Xj[110X appears in [10Xinn[i][110X each time
  there exists an edge [10X[j,i][110X in [3Xdigraph[103X.[133X
  
  [33X[0;0YThe  function  [10XInNeighbours[110X  returns an immutable list of lists, whereas the
  function  [10XInNeighboursMutableCopy[110X  returns a copy of [10XInNeighbours[110X which is a
  mutable list of mutable lists.[133X
  
  [33X[0;0YNote  that  the  entries  of  [10Xinn[110X  are not necessarily sorted into ascending
  order,  particularly  if  [3Xdigraph[103X  was constructed via [2XDigraphByInNeighbours[102X
  ([14X3.1-11[114X).[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xgr := Digraph(["a", "b", "c"],[127X[104X
    [4X[25X>[125X [27X                 ["a", "b", "b"],[127X[104X
    [4X[25X>[125X [27X                 ["b", "a", "c"]);[127X[104X
    [4X[28X<immutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XInNeighbours(gr);[127X[104X
    [4X[28X[ [ 2 ], [ 1 ], [ 2 ] ][128X[104X
    [4X[25Xgap>[125X [27Xgr := Digraph([[1, 2, 3], [2, 1], [3]]);[127X[104X
    [4X[28X<immutable digraph with 3 vertices, 6 edges>[128X[104X
    [4X[25Xgap>[125X [27XInNeighbours(gr);[127X[104X
    [4X[28X[ [ 1, 2 ], [ 1, 2 ], [ 1, 3 ] ][128X[104X
    [4X[25Xgap>[125X [27Xgr := DigraphByAdjacencyMatrix([[127X[104X
    [4X[25X>[125X [27X [1, 2, 1],[127X[104X
    [4X[25X>[125X [27X [1, 1, 0],[127X[104X
    [4X[25X>[125X [27X [0, 0, 1]]);[127X[104X
    [4X[28X<immutable multidigraph with 3 vertices, 7 edges>[128X[104X
    [4X[25Xgap>[125X [27XInNeighbours(gr);[127X[104X
    [4X[28X[ [ 1, 2 ], [ 1, 1, 2 ], [ 1, 3 ] ][128X[104X
    [4X[25Xgap>[125X [27XInNeighboursMutableCopy(gr);[127X[104X
    [4X[28X[ [ 1, 2 ], [ 1, 1, 2 ], [ 1, 3 ] ][128X[104X
    [4X[25Xgap>[125X [27XD := CycleDigraph(IsMutableDigraph, 3);[127X[104X
    [4X[28X<mutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XInNeighbours(D);[127X[104X
    [4X[28X[ [ 3 ], [ 1 ], [ 2 ] ][128X[104X
  [4X[32X[104X
  
  [1X5.2-8 OutDegrees[101X
  
  [33X[1;0Y[29X[2XOutDegrees[102X( [3Xdigraph[103X ) [32X attribute[133X
  [33X[1;0Y[29X[2XOutDegreeSequence[102X( [3Xdigraph[103X ) [32X attribute[133X
  [33X[1;0Y[29X[2XOutDegreeSet[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA list of non-negative integers.[133X
  
  [33X[0;0YGiven  a digraph [3Xdigraph[103X with [22Xn[122X vertices, the function [10XOutDegrees[110X returns an
  immutable  list  [10Xout[110X  of  length [22Xn[122X, such that for a vertex [10Xi[110X in [3Xdigraph[103X, the
  value  of  [10Xout[i][110X  is  the  out-degree  of  vertex  [10Xi[110X. See [2XOutDegreeOfVertex[102X
  ([14X5.2-10[114X).[133X
  
  [33X[0;0YThe  function  [10XOutDegreeSequence[110X  returns  the  same list, after it has been
  sorted into non-increasing order.[133X
  
  [33X[0;0YThe  function  [10XOutDegreeSet[110X  returns  the  same list, sorted into increasing
  order with duplicate entries removed.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[1, 3, 2, 2], [], [2, 1], []]);[127X[104X
    [4X[28X<immutable multidigraph with 4 vertices, 6 edges>[128X[104X
    [4X[25Xgap>[125X [27XOutDegrees(D);[127X[104X
    [4X[28X[ 4, 0, 2, 0 ][128X[104X
    [4X[25Xgap>[125X [27XOutDegreeSequence(D);[127X[104X
    [4X[28X[ 4, 2, 0, 0 ][128X[104X
    [4X[25Xgap>[125X [27XOutDegreeSet(D);[127X[104X
    [4X[28X[ 0, 2, 4 ][128X[104X
    [4X[25Xgap>[125X [27XD := CycleDigraph(IsMutableDigraph, 3);[127X[104X
    [4X[28X<mutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XOutDegrees(D);[127X[104X
    [4X[28X[ 1, 1, 1 ][128X[104X
  [4X[32X[104X
  
  [1X5.2-9 InDegrees[101X
  
  [33X[1;0Y[29X[2XInDegrees[102X( [3Xdigraph[103X ) [32X attribute[133X
  [33X[1;0Y[29X[2XInDegreeSequence[102X( [3Xdigraph[103X ) [32X attribute[133X
  [33X[1;0Y[29X[2XInDegreeSet[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA list of non-negative integers.[133X
  
  [33X[0;0YGiven  a  digraph [3Xdigraph[103X with [22Xn[122X vertices, the function [10XInDegrees[110X returns an
  immutable  list  [10Xinn[110X  of  length [22Xn[122X, such that for a vertex [10Xi[110X in [3Xdigraph[103X, the
  value of [10Xinn[i][110X is the in-degree of vertex [10Xi[110X. See [2XInDegreeOfVertex[102X ([14X5.2-12[114X).[133X
  
  [33X[0;0YThe  function  [10XInDegreeSequence[110X  returns  the  same  list, after it has been
  sorted into non-increasing order.[133X
  
  [33X[0;0YThe function [10XInDegreeSet[110X returns the same list, sorted into increasing order
  with duplicate entries removed.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[1, 3, 2, 2, 4], [], [2, 1, 4], []]);[127X[104X
    [4X[28X<immutable multidigraph with 4 vertices, 8 edges>[128X[104X
    [4X[25Xgap>[125X [27XInDegrees(D);[127X[104X
    [4X[28X[ 2, 3, 1, 2 ][128X[104X
    [4X[25Xgap>[125X [27XInDegreeSequence(D);[127X[104X
    [4X[28X[ 3, 2, 2, 1 ][128X[104X
    [4X[25Xgap>[125X [27XInDegreeSet(D);[127X[104X
    [4X[28X[ 1, 2, 3 ][128X[104X
    [4X[25Xgap>[125X [27XD := CycleDigraph(IsMutableDigraph, 3);[127X[104X
    [4X[28X<mutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XInDegrees(D);[127X[104X
    [4X[28X[ 1, 1, 1 ][128X[104X
  [4X[32X[104X
  
  [1X5.2-10 OutDegreeOfVertex[101X
  
  [33X[1;0Y[29X[2XOutDegreeOfVertex[102X( [3Xdigraph[103X, [3Xvertex[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10YThe non-negative integer.[133X
  
  [33X[0;0YThis  operation  returns  the out-degree of the vertex [3Xvertex[103X in the digraph
  [3Xdigraph[103X.  The  out-degree  of [3Xvertex[103X is the number of edges in [3Xdigraph[103X whose
  source is [3Xvertex[103X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[127X[104X
    [4X[25X>[125X [27X[2, 2, 1], [1, 4], [2, 2, 4, 2], [1, 1, 2, 2, 1, 2, 2]]);[127X[104X
    [4X[28X<immutable multidigraph with 4 vertices, 16 edges>[128X[104X
    [4X[25Xgap>[125X [27XOutDegreeOfVertex(D, 1);[127X[104X
    [4X[28X3[128X[104X
    [4X[25Xgap>[125X [27XOutDegreeOfVertex(D, 2);[127X[104X
    [4X[28X2[128X[104X
    [4X[25Xgap>[125X [27XOutDegreeOfVertex(D, 3);[127X[104X
    [4X[28X4[128X[104X
    [4X[25Xgap>[125X [27XOutDegreeOfVertex(D, 4);[127X[104X
    [4X[28X7[128X[104X
  [4X[32X[104X
  
  [1X5.2-11 OutNeighboursOfVertex[101X
  
  [33X[1;0Y[29X[2XOutNeighboursOfVertex[102X( [3Xdigraph[103X, [3Xvertex[103X ) [32X operation[133X
  [33X[1;0Y[29X[2XOutNeighborsOfVertex[102X( [3Xdigraph[103X, [3Xvertex[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10YA list of vertices.[133X
  
  [33X[0;0YThis  operation  returns  the list [10Xout[110X of vertices of the digraph [3Xdigraph[103X. A
  vertex  [10Xi[110X appears in the list [10Xout[110X each time there exists an edge with source
  [3Xvertex[103X  and  range  [10Xi[110X  in  [3Xdigraph[103X;  in  particular, this means that [10Xout[110X may
  contain duplicates.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[127X[104X
    [4X[25X>[125X [27X[2, 2, 3], [1, 3, 4], [2, 2, 3], [1, 1, 2, 2, 1, 2, 2]]);[127X[104X
    [4X[28X<immutable multidigraph with 4 vertices, 16 edges>[128X[104X
    [4X[25Xgap>[125X [27XOutNeighboursOfVertex(D, 1);[127X[104X
    [4X[28X[ 2, 2, 3 ][128X[104X
    [4X[25Xgap>[125X [27XOutNeighboursOfVertex(D, 3);[127X[104X
    [4X[28X[ 2, 2, 3 ][128X[104X
  [4X[32X[104X
  
  [1X5.2-12 InDegreeOfVertex[101X
  
  [33X[1;0Y[29X[2XInDegreeOfVertex[102X( [3Xdigraph[103X, [3Xvertex[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10YA non-negative integer.[133X
  
  [33X[0;0YThis  operation  returns  the  in-degree of the vertex [3Xvertex[103X in the digraph
  [3Xdigraph[103X.  The  in-degree  of  [3Xvertex[103X is the number of edges in [3Xdigraph[103X whose
  range is [3Xvertex[103X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[127X[104X
    [4X[25X>[125X [27X[2, 2, 1], [1, 4], [2, 2, 4, 2], [1, 1, 2, 2, 1, 2, 2]]);[127X[104X
    [4X[28X<immutable multidigraph with 4 vertices, 16 edges>[128X[104X
    [4X[25Xgap>[125X [27XInDegreeOfVertex(D, 1);[127X[104X
    [4X[28X5[128X[104X
    [4X[25Xgap>[125X [27XInDegreeOfVertex(D, 2);[127X[104X
    [4X[28X9[128X[104X
    [4X[25Xgap>[125X [27XInDegreeOfVertex(D, 3);[127X[104X
    [4X[28X0[128X[104X
    [4X[25Xgap>[125X [27XInDegreeOfVertex(D, 4);[127X[104X
    [4X[28X2[128X[104X
  [4X[32X[104X
  
  [1X5.2-13 InNeighboursOfVertex[101X
  
  [33X[1;0Y[29X[2XInNeighboursOfVertex[102X( [3Xdigraph[103X, [3Xvertex[103X ) [32X operation[133X
  [33X[1;0Y[29X[2XInNeighborsOfVertex[102X( [3Xdigraph[103X, [3Xvertex[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10YA list of postitive vertices.[133X
  
  [33X[0;0YThis  operation  returns  the list [10Xinn[110X of vertices of the digraph [3Xdigraph[103X. A
  vertex  [10Xi[110X appears in the list [10Xinn[110X each time there exists an edge with source
  [10Xi[110X  and  range  [3Xvertex[103X  in  [3Xdigraph[103X;  in  particular, this means that [10Xinn[110X may
  contain duplicates.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[127X[104X
    [4X[25X>[125X [27X[2, 2, 3], [1, 3, 4], [2, 2, 3], [1, 1, 2, 2, 1, 2, 2]]);[127X[104X
    [4X[28X<immutable multidigraph with 4 vertices, 16 edges>[128X[104X
    [4X[25Xgap>[125X [27XInNeighboursOfVertex(D, 1);[127X[104X
    [4X[28X[ 2, 4, 4, 4 ][128X[104X
    [4X[25Xgap>[125X [27XInNeighboursOfVertex(D, 2);[127X[104X
    [4X[28X[ 1, 1, 3, 3, 4, 4, 4, 4 ][128X[104X
  [4X[32X[104X
  
  [1X5.2-14 DigraphLoops[101X
  
  [33X[1;0Y[29X[2XDigraphLoops[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA list of vertices.[133X
  
  [33X[0;0YIf  [3Xdigraph[103X  is  a digraph, then [10XDigraphLoops[110X returns the list consisting of
  the  [2XDigraphVertices[102X  ([14X5.1-1[114X)  of  [3Xdigraph[103X  at  which  there  is a loop. See
  [2XDigraphHasLoops[102X ([14X6.2-1[114X).[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[2], [3], []]);[127X[104X
    [4X[28X<immutable digraph with 3 vertices, 2 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphHasLoops(D);[127X[104X
    [4X[28Xfalse[128X[104X
    [4X[25Xgap>[125X [27XDigraphLoops(D);[127X[104X
    [4X[28X[  ][128X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[3, 5], [1], [2, 4, 3], [4], [2, 1]]);[127X[104X
    [4X[28X<immutable digraph with 5 vertices, 9 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphLoops(D);[127X[104X
    [4X[28X[ 3, 4 ][128X[104X
    [4X[25Xgap>[125X [27XD := Digraph(IsMutableDigraph, [[1], [1]]);[127X[104X
    [4X[28X<mutable digraph with 2 vertices, 2 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphLoops(D);[127X[104X
    [4X[28X[ 1 ][128X[104X
  [4X[32X[104X
  
  [1X5.2-15 DegreeMatrix[101X
  
  [33X[1;0Y[29X[2XDegreeMatrix[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA square matrix of non-negative integers.[133X
  
  [33X[0;0YReturns  the  out-degree matrix [10Xmat[110X of the digraph [3Xdigraph[103X. The value of the
  [10Xi[110Xth  diagonal matrix entry is the out-degree of the vertex [10Xi[110X in [3Xdigraph[103X. All
  off-diagonal  entries are [10X0[110X. If [3Xdigraph[103X has no vertices, then the empty list
  is returned.[133X
  
  [33X[0;0YSee [2XOutDegrees[102X ([14X5.2-8[114X) for more information.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[1, 2, 3], [4], [1, 3, 4], []]);[127X[104X
    [4X[28X<immutable digraph with 4 vertices, 7 edges>[128X[104X
    [4X[25Xgap>[125X [27XPrintArray(DegreeMatrix(D));[127X[104X
    [4X[28X[ [  3,  0,  0,  0 ],[128X[104X
    [4X[28X  [  0,  1,  0,  0 ],[128X[104X
    [4X[28X  [  0,  0,  3,  0 ],[128X[104X
    [4X[28X  [  0,  0,  0,  0 ] ][128X[104X
    [4X[25Xgap>[125X [27XD := CycleDigraph(5);;[127X[104X
    [4X[25Xgap>[125X [27XPrintArray(DegreeMatrix(D));[127X[104X
    [4X[28X[ [  1,  0,  0,  0,  0 ],[128X[104X
    [4X[28X  [  0,  1,  0,  0,  0 ],[128X[104X
    [4X[28X  [  0,  0,  1,  0,  0 ],[128X[104X
    [4X[28X  [  0,  0,  0,  1,  0 ],[128X[104X
    [4X[28X  [  0,  0,  0,  0,  1 ] ][128X[104X
    [4X[25Xgap>[125X [27XDegreeMatrix(EmptyDigraph(0));[127X[104X
    [4X[28X[  ][128X[104X
    [4X[25Xgap>[125X [27XD := CycleDigraph(IsMutableDigraph, 3);[127X[104X
    [4X[28X<mutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XDisplay(DegreeMatrix(D));[127X[104X
    [4X[28X[ [  1,  0,  0 ],[128X[104X
    [4X[28X  [  0,  1,  0 ],[128X[104X
    [4X[28X  [  0,  0,  1 ] ][128X[104X
  [4X[32X[104X
  
  [1X5.2-16 LaplacianMatrix[101X
  
  [33X[1;0Y[29X[2XLaplacianMatrix[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA square matrix of integers.[133X
  
  [33X[0;0YReturns  the  out-degree  Laplacian  matrix  [10Xmat[110X of the digraph [3Xdigraph[103X. The
  out-degree   Laplacian   matrix   is   defined  as  [10XDegreeMatrix(digraph)  -
  AdjacencyMatrix(digraph)[110X. If [3Xdigraph[103X has no vertices, then the empty list is
  returned.[133X
  
  [33X[0;0YSee [2XDegreeMatrix[102X ([14X5.2-15[114X) and [2XAdjacencyMatrix[102X ([14X5.2-1[114X) for more information.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xgr := Digraph([[1, 2, 3], [4], [1, 3, 4], []]);[127X[104X
    [4X[28X<immutable digraph with 4 vertices, 7 edges>[128X[104X
    [4X[25Xgap>[125X [27XPrintArray(LaplacianMatrix(gr));[127X[104X
    [4X[28X[ [   2,  -1,  -1,   0 ],[128X[104X
    [4X[28X  [   0,   1,   0,  -1 ],[128X[104X
    [4X[28X  [  -1,   0,   2,  -1 ],[128X[104X
    [4X[28X  [   0,   0,   0,   0 ] ][128X[104X
    [4X[25Xgap>[125X [27XLaplacianMatrix(EmptyDigraph(0));[127X[104X
    [4X[28X[  ][128X[104X
    [4X[25Xgap>[125X [27XD := CycleDigraph(IsMutableDigraph, 3);[127X[104X
    [4X[28X<mutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XDisplay(LaplacianMatrix(D));[127X[104X
    [4X[28X[ [   1,  -1,   0 ],[128X[104X
    [4X[28X  [   0,   1,  -1 ],[128X[104X
    [4X[28X  [  -1,   0,   1 ] ][128X[104X
  [4X[32X[104X
  
  
  [1X5.3 [33X[0;0YOrders[133X[101X
  
  [1X5.3-1 PartialOrderDigraphMeetOfVertices[101X
  
  [33X[1;0Y[29X[2XPartialOrderDigraphMeetOfVertices[102X( [3Xdigraph[103X, [3Xu[103X, [3Xv[103X ) [32X operation[133X
  [33X[1;0Y[29X[2XPartialOrderDigraphJoinOfVertices[102X( [3Xdigraph[103X, [3Xu[103X, [3Xv[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10YA positive integer or [9Xfail[109X[133X
  
  [33X[0;0YIf  the  first  argument  is  a  partial order digraph [2XIsPartialOrderDigraph[102X
  ([14X6.3-2[114X) then these operations return the meet, or the join, of the two input
  vertices. If the meet (or join) is does not exist then [9Xfail[109X is returned. The
  meet  (or  join)  is  guaranteed  to exist when the first argument satisfies
  [2XIsMeetSemilatticeDigraph[102X ([14X6.3-3[114X) (or [2XIsJoinSemilatticeDigraph[102X ([14X6.3-3[114X)) - see
  the  documentation  for  these properties for the definition of the meet (or
  the join).[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[1], [1, 2], [1, 3], [1, 2, 3, 4]]);[127X[104X
    [4X[28X<immutable digraph with 4 vertices, 9 edges>[128X[104X
    [4X[25Xgap>[125X [27XPartialOrderDigraphMeetOfVertices(D, 2, 3);[127X[104X
    [4X[28X4[128X[104X
    [4X[25Xgap>[125X [27XPartialOrderDigraphJoinOfVertices(D, 2, 3);[127X[104X
    [4X[28X1[128X[104X
    [4X[25Xgap>[125X [27XPartialOrderDigraphMeetOfVertices(D, 1, 2);[127X[104X
    [4X[28X2[128X[104X
    [4X[25Xgap>[125X [27XPartialOrderDigraphJoinOfVertices(D, 3, 4);[127X[104X
    [4X[28X3[128X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[1], [2], [1, 2, 3], [1, 2, 4]]);[127X[104X
    [4X[28X<immutable digraph with 4 vertices, 8 edges>[128X[104X
    [4X[25Xgap>[125X [27XPartialOrderDigraphMeetOfVertices(D, 3, 4);[127X[104X
    [4X[28Xfail[128X[104X
    [4X[25Xgap>[125X [27XPartialOrderDigraphJoinOfVertices(D, 3, 4);[127X[104X
    [4X[28Xfail[128X[104X
    [4X[25Xgap>[125X [27XPartialOrderDigraphMeetOfVertices(D, 1, 2);[127X[104X
    [4X[28Xfail[128X[104X
    [4X[25Xgap>[125X [27XPartialOrderDigraphJoinOfVertices(D, 1, 2);[127X[104X
    [4X[28Xfail[128X[104X
  [4X[32X[104X
  
  [1X5.3-2 NonUpperSemimodularPair[101X
  
  [33X[1;0Y[29X[2XNonUpperSemimodularPair[102X( [3XD[103X ) [32X attribute[133X
  [33X[1;0Y[29X[2XNonLowerSemimodularPair[102X( [3XD[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA pair of vertices or [9Xfail[109X.[133X
  
  [33X[0;0Y[10XNonUpperSemimodularPair[110X  returns  a  pair  of vertices in the digraph [3XD[103X that
  witnesses  the  fact that [3XD[103X does not represent an upper semimodular lattice,
  if such a pair exists.[133X
  
  [33X[0;0YIf the digraph [3XD[103X does not satisfy [2XIsLatticeDigraph[102X ([14X6.3-3[114X), then an error is
  given.  Otherwise  if  the  digraph [3XD[103X does satisfy [2XIsLatticeDigraph[102X ([14X6.3-3[114X),
  then either a non-upper semimodular pair of vertices is returned, or [9Xfail[109X is
  returned  if  no  such  pair  exists (meaning that [3XD[103X is an upper semimodular
  lattice.[133X
  
  [33X[0;0Y[10XNonLowerSemimodularPair[110X     behaves     in     the    analogous    way    to
  [10XNonUpperSemimodularPair[110X with respect to lower semimodularity.[133X
  
  [33X[0;0YSee  [2XIsUpperSemimodularDigraph[102X ([14X6.3-5[114X) and [2XIsLowerSemimodularDigraph[102X ([14X6.3-5[114X)
  for the definition of upper semimodularity of a lattice.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := DigraphFromDigraph6String([127X[104X
    [4X[25X>[125X [27X"&M~~sc`lYUZO__KIBboC_@h?U_?_GL?A_?c");[127X[104X
    [4X[28X<immutable digraph with 14 vertices, 66 edges>[128X[104X
    [4X[25Xgap>[125X [27XNonLowerSemimodularPair(D);[127X[104X
    [4X[28X[ 10, 9 ][128X[104X
    [4X[25Xgap>[125X [27XNonUpperSemimodularPair(D);[127X[104X
    [4X[28Xfail[128X[104X
  [4X[32X[104X
  
  
  [1X5.4 [33X[0;0YReachability and connectivity[133X[101X
  
  [1X5.4-1 DigraphDiameter[101X
  
  [33X[1;0Y[29X[2XDigraphDiameter[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YAn integer or [10Xfail[110X.[133X
  
  [33X[0;0YThis function returns the diameter of the digraph [3Xdigraph[103X.[133X
  
  [33X[0;0YIf  a  digraph [3Xdigraph[103X is strongly connected and has at least 1 vertex, then
  the  [13Xdiameter[113X  is the maximum shortest distance between any pair of distinct
  vertices.  Otherwise  then  the  diameter  of [3Xdigraph[103X is undefined, and this
  function returns the value [10Xfail[110X.[133X
  
  [33X[0;0YSee [2XDigraphShortestDistances[102X ([14X5.4-3[114X).[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[2], [3], [4, 5], [5], [1, 2, 3, 4, 5]]);[127X[104X
    [4X[28X<immutable digraph with 5 vertices, 10 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphDiameter(D);[127X[104X
    [4X[28X3[128X[104X
    [4X[25Xgap>[125X [27XD := ChainDigraph(2);[127X[104X
    [4X[28X<immutable chain digraph with 2 vertices>[128X[104X
    [4X[25Xgap>[125X [27XDigraphDiameter(D);[127X[104X
    [4X[28Xfail[128X[104X
    [4X[25Xgap>[125X [27XIsStronglyConnectedDigraph(D);[127X[104X
    [4X[28Xfalse[128X[104X
    [4X[25Xgap>[125X [27XD := GeneralisedPetersenGraph(IsMutableDigraph, 6, 2);[127X[104X
    [4X[28X<mutable digraph with 12 vertices, 36 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphDiameter(D);[127X[104X
    [4X[28X4[128X[104X
  [4X[32X[104X
  
  [1X5.4-2 DigraphShortestDistance[101X
  
  [33X[1;0Y[29X[2XDigraphShortestDistance[102X( [3Xdigraph[103X, [3Xu[103X, [3Xv[103X ) [32X operation[133X
  [33X[1;0Y[29X[2XDigraphShortestDistance[102X( [3Xdigraph[103X, [3Xlist[103X ) [32X operation[133X
  [33X[1;0Y[29X[2XDigraphShortestDistance[102X( [3Xdigraph[103X, [3Xlist1[103X, [3Xlist2[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10YAn integer or [9Xfail[109X[133X
  
  [33X[0;0YIf  there  is  a  directed  path in the digraph [3Xdigraph[103X between vertex [3Xu[103X and
  vertex  [3Xv[103X,  then  this  operation  returns  the  length of the shortest such
  directed  path. If no such directed path exists, then this operation returns
  [9Xfail[109X. See Section [14X1.1-1[114X for the definition of a directed path.[133X
  
  [33X[0;0YIf  the  second  form  is  used,  then  [3Xlist[103X should be a list of length two,
  containing two positive integers which correspond to the vertices [3Xu[103X and [3Xv[103X.[133X
  
  [33X[0;0YNote that as usual, a vertex is considered to be at distance 0 from itself .[133X
  
  [33X[0;0YIf  the third form is used, then [3Xlist1[103X and [3Xlist2[103X are both lists of vertices.
  The shortest directed path between [3Xlist1[103X and [3Xlist2[103X is then the length of the
  shortest directed path which starts with a vertex in [3Xlist1[103X and terminates at
  a  vertex  in  [3Xlist2[103X,  if such directed path exists. If [3Xlist1[103X and [3Xlist2[103X have
  non-empty intersection, the operation returns [10X0[110X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[2], [3], [1, 4], [1, 3], [5]]);[127X[104X
    [4X[28X<immutable digraph with 5 vertices, 7 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphShortestDistance(D, 1, 3);[127X[104X
    [4X[28X2[128X[104X
    [4X[25Xgap>[125X [27XDigraphShortestDistance(D, [3, 3]);[127X[104X
    [4X[28X0[128X[104X
    [4X[25Xgap>[125X [27XDigraphShortestDistance(D, 5, 2);[127X[104X
    [4X[28Xfail[128X[104X
    [4X[25Xgap>[125X [27XDigraphShortestDistance(D, [1, 2], [4, 5]);[127X[104X
    [4X[28X2[128X[104X
    [4X[25Xgap>[125X [27XDigraphShortestDistance(D, [1, 3], [3, 5]);[127X[104X
    [4X[28X0[128X[104X
  [4X[32X[104X
  
  [1X5.4-3 DigraphShortestDistances[101X
  
  [33X[1;0Y[29X[2XDigraphShortestDistances[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA square matrix.[133X
  
  [33X[0;0YIf [3Xdigraph[103X is a digraph with [22Xn[122X vertices, then this function returns an [22Xn × n[122X
  matrix [10Xmat[110X, where each entry is either a non-negative integer, or [9Xfail[109X. If [22Xn
  = 0[122X, then an empty list is returned.[133X
  
  [33X[0;0YIf  there  is  a  directed path from vertex [10Xi[110X to vertex [10Xj[110X, then the value of
  [10Xmat[i][j][110X  is  the  length  of  the  shortest such directed path. If no such
  directed  path  exists,  then  the  value  of  [10Xmat[i][j][110X is [10Xfail[110X. We use the
  convention  that  the  distance  from  every  vertex  to  itself  is [10X0[110X, i.e.
  [10Xmat[i][i] = 0[110X for all vertices [10Xi[110X.[133X
  
  [33X[0;0YThe  method  used  in  this  function  is  a  version  of the Floyd-Warshall
  algorithm, and has complexity [22XO(n^3)[122X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[1, 2], [3], [1, 2], [4]]);[127X[104X
    [4X[28X<immutable digraph with 4 vertices, 6 edges>[128X[104X
    [4X[25Xgap>[125X [27Xmat := DigraphShortestDistances(D);;[127X[104X
    [4X[25Xgap>[125X [27XPrintArray(mat);[127X[104X
    [4X[28X[ [     0,     1,     2,  fail ],[128X[104X
    [4X[28X  [     2,     0,     1,  fail ],[128X[104X
    [4X[28X  [     1,     1,     0,  fail ],[128X[104X
    [4X[28X  [  fail,  fail,  fail,     0 ] ][128X[104X
    [4X[25Xgap>[125X [27XD := CycleDigraph(IsMutableDigraph, 3);[127X[104X
    [4X[28X<mutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphShortestDistances(D);[127X[104X
    [4X[28X[ [ 0, 1, 2 ], [ 2, 0, 1 ], [ 1, 2, 0 ] ][128X[104X
  [4X[32X[104X
  
  [1X5.4-4 DigraphLongestDistanceFromVertex[101X
  
  [33X[1;0Y[29X[2XDigraphLongestDistanceFromVertex[102X( [3Xdigraph[103X, [3Xv[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10YAn integer, or [9Xinfinity[109X.[133X
  
  [33X[0;0YIf  [3Xdigraph[103X  is  a digraph and [3Xv[103X is a vertex in [3Xdigraph[103X, then this operation
  returns  the  length of the longest directed walk in [3Xdigraph[103X which begins at
  vertex  [3Xv[103X.  See Section [14X1.1-1[114X for the definitions of directed walk, directed
  cycle, and loop.[133X
  
  [30X    [33X[0;6YIf there exists a directed walk starting at vertex [3Xv[103X which traverses a
        loop  or  a  directed  cycle,  then  we consider there to be a walk of
        infinite   length  from  [3Xv[103X  (realised  by  repeatedly  traversing  the
        loop/directed cycle), and so the result is [9Xinfinity[109X. To disallow walks
        using loops, try using [2XDigraphRemoveLoops[102X ([14X3.3-25[114X):[133X
  
        [33X[0;6Y[10XDigraphLongestDistanceFromVertex(DigraphRemoveLoops([3Xdigraph[103X[10X,[3Xv[103X[10X))[110X.[133X
  
  [30X    [33X[0;6YOtherwise,  if  all  directed  walks  starting at vertex [3Xv[103X have finite
        length, then the length of the longest such walk is returned.[133X
  
  [33X[0;0YNote  that  the  result  is  [10X0[110X  if  and  only if [3Xv[103X is a sink of [3Xdigraph[103X. See
  [2XDigraphSinks[102X ([14X5.1-6[114X).[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[2], [3, 4], [], [5], [], [6]]);[127X[104X
    [4X[28X<immutable digraph with 6 vertices, 5 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphLongestDistanceFromVertex(D, 1);[127X[104X
    [4X[28X3[128X[104X
    [4X[25Xgap>[125X [27XDigraphLongestDistanceFromVertex(D, 3);[127X[104X
    [4X[28X0[128X[104X
    [4X[25Xgap>[125X [27X3 in DigraphSinks(D);[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27XDigraphLongestDistanceFromVertex(D, 6);[127X[104X
    [4X[28Xinfinity[128X[104X
  [4X[32X[104X
  
  [1X5.4-5 DigraphDistanceSet[101X
  
  [33X[1;0Y[29X[2XDigraphDistanceSet[102X( [3Xdigraph[103X, [3Xvertex[103X, [3Xdistance[103X ) [32X operation[133X
  [33X[1;0Y[29X[2XDigraphDistanceSet[102X( [3Xdigraph[103X, [3Xvertex[103X, [3Xdistances[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10YA list of vertices[133X
  
  [33X[0;0YThis operation returns the list of all vertices in digraph [3Xdigraph[103X such that
  the  shortest  distance  to  a  vertex  [3Xvertex[103X is [3Xdistance[103X or is in the list
  [3Xdistances[103X.[133X
  
  [33X[0;0Y[3Xdigraph[103X  should  be a digraph, [3Xvertex[103X should be a positive integer, [3Xdistance[103X
  should  be  a  non-negative  integer,  and  [3Xdistances[103X  should  be  a list of
  non-negative integers.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[2], [3], [1, 4], [1, 3]]);[127X[104X
    [4X[28X<immutable digraph with 4 vertices, 6 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphDistanceSet(D, 2, [1, 2]);[127X[104X
    [4X[28X[ 3, 1, 4 ][128X[104X
    [4X[25Xgap>[125X [27XDigraphDistanceSet(D, 3, 1);[127X[104X
    [4X[28X[ 1, 4 ][128X[104X
    [4X[25Xgap>[125X [27XDigraphDistanceSet(D, 2, 0);[127X[104X
    [4X[28X[ 2 ][128X[104X
  [4X[32X[104X
  
  [1X5.4-6 DigraphGirth[101X
  
  [33X[1;0Y[29X[2XDigraphGirth[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YAn integer, or [9Xinfinity[109X.[133X
  
  [33X[0;0YThis  attribute  returns  the  [13Xgirth[113X  of the digraph [3Xdigraph[103X. The [13Xgirth[113X of a
  digraph  is the length of its shortest simple circuit. See Section [14X1.1-1[114X for
  the definitions of simple circuit, directed cycle, and loop.[133X
  
  [33X[0;0YIf  [3Xdigraph[103X has no directed cycles, then this function will return [9Xinfinity[109X.
  If [3Xdigraph[103X contains a loop, then this function will return [10X1[110X.[133X
  
  [33X[0;0YIn  the  worst  case,  the  method used in this function is a version of the
  Floyd-Warshall algorithm, and has complexity [10XO([3Xn[103X[10X ^ 3)[110X, where [3Xn[103X is the number
  of  vertices  in  [3Xdigraph[103X.  If  the  digraph  has  known  automorphisms [see
  [2XDigraphGroup[102X ([14X7.2-10[114X)], then the performance is likely to be better.[133X
  
  [33X[0;0YFor symmetric digraphs, see also [2XDigraphUndirectedGirth[102X ([14X5.4-8[114X).[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[1], [1]]);[127X[104X
    [4X[28X<immutable digraph with 2 vertices, 2 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphGirth(D);[127X[104X
    [4X[28X1[128X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[2, 3], [3], [4], []]);[127X[104X
    [4X[28X<immutable digraph with 4 vertices, 4 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphGirth(D);[127X[104X
    [4X[28Xinfinity[128X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[2, 3], [3], [4], [1]]);[127X[104X
    [4X[28X<immutable digraph with 4 vertices, 5 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphGirth(D);[127X[104X
    [4X[28X3[128X[104X
    [4X[25Xgap>[125X [27XD := GeneralisedPetersenGraph(IsMutableDigraph, 6, 2);[127X[104X
    [4X[28X<mutable digraph with 12 vertices, 36 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphGirth(D);[127X[104X
    [4X[28X2[128X[104X
  [4X[32X[104X
  
  [1X5.4-7 DigraphOddGirth[101X
  
  [33X[1;0Y[29X[2XDigraphOddGirth[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YAn integer, or [9Xinfinity[109X.[133X
  
  [33X[0;0YThis  attribute  returns the [13Xodd girth[113X of the digraph [3Xdigraph[103X. The [13Xodd girth[113X
  of a digraph is the length of its shortest simple circuit of odd length. See
  Section  [14X1.1-1[114X  for  the  definitions of simple circuit, directed cycle, and
  loop.[133X
  
  [33X[0;0YIf  [3Xdigraph[103X  has  no  directed cycles of odd length, then this function will
  return  [9Xinfinity[109X,  even  if  [3Xdigraph[103X has a directed cycle of even length. If
  [3Xdigraph[103X contains a loop, then this function will return [10X1[110X.[133X
  
  [33X[0;0YSee also [2XDigraphGirth[102X ([14X5.4-6[114X).[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[2], [3, 1], [1]]);[127X[104X
    [4X[28X<immutable digraph with 3 vertices, 4 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphOddGirth(D);[127X[104X
    [4X[28X3[128X[104X
    [4X[25Xgap>[125X [27XD := CycleDigraph(4);[127X[104X
    [4X[28X<immutable cycle digraph with 4 vertices>[128X[104X
    [4X[25Xgap>[125X [27XDigraphOddGirth(D);[127X[104X
    [4X[28Xinfinity[128X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[2], [3], [], [3], [4]]);[127X[104X
    [4X[28X<immutable digraph with 5 vertices, 4 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphOddGirth(D);[127X[104X
    [4X[28Xinfinity[128X[104X
    [4X[25Xgap>[125X [27XD := CycleDigraph(IsMutableDigraph, 4);[127X[104X
    [4X[28X<mutable digraph with 4 vertices, 4 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphDisjointUnion(D, CycleDigraph(5));[127X[104X
    [4X[28X<mutable digraph with 9 vertices, 9 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphOddGirth(D);[127X[104X
    [4X[28X5[128X[104X
  [4X[32X[104X
  
  [1X5.4-8 DigraphUndirectedGirth[101X
  
  [33X[1;0Y[29X[2XDigraphUndirectedGirth[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YAn integer or [9Xinfinity[109X.[133X
  
  [33X[0;0YIf  [3Xdigraph[103X  is a symmetric digraph, then this function returns the girth of
  [3Xdigraph[103X  when treated as an undirected graph (i.e. each pair of edges [22X[i, j][122X
  and [22X[j, i][122X is treated as a single edge between [22Xi[122X and [22Xj[122X).[133X
  
  [33X[0;0YThe [13Xgirth[113X of an undirected graph is the length of its shortest simple cycle,
  i.e.  the  shortest  non-trivial path starting and ending at the same vertex
  and passing through no vertex or edge more than once.[133X
  
  [33X[0;0YIf [3Xdigraph[103X has no cycles, then this function will return [9Xinfinity[109X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[2, 4], [1, 3], [2, 4], [1, 3]]);[127X[104X
    [4X[28X<immutable digraph with 4 vertices, 8 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphUndirectedGirth(D);[127X[104X
    [4X[28X4[128X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[2], [1, 3], [2]]);[127X[104X
    [4X[28X<immutable digraph with 3 vertices, 4 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphUndirectedGirth(D);[127X[104X
    [4X[28Xinfinity[128X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[1], [], [4], [3]]);[127X[104X
    [4X[28X<immutable digraph with 4 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphUndirectedGirth(D);[127X[104X
    [4X[28X1[128X[104X
    [4X[25Xgap>[125X [27XD := GeneralisedPetersenGraph(IsMutableDigraph, 9, 2);[127X[104X
    [4X[28X<mutable digraph with 18 vertices, 54 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphUndirectedGirth(D);[127X[104X
    [4X[28X5[128X[104X
  [4X[32X[104X
  
  [1X5.4-9 DigraphConnectedComponents[101X
  
  [33X[1;0Y[29X[2XDigraphConnectedComponents[102X( [3Xdigraph[103X ) [32X attribute[133X
  [33X[1;0Y[29X[2XDigraphNrConnectedComponents[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA record.[133X
  
  [33X[0;0YThis  function  returns the record [10Xwcc[110X corresponding to the weakly connected
  components  of  the digraph [3Xdigraph[103X. Two vertices of [3Xdigraph[103X are in the same
  weakly  connected  component  whenever  they  are  equal,  or there exists a
  directed  path  (ignoring  the  orientation  of  edges)  between  them. More
  formally, two vertices are in the same weakly connected component of [3Xdigraph[103X
  if  and  only  if  they  are  in  the same strongly connected component (see
  [2XDigraphStronglyConnectedComponents[102X  ([14X5.4-11[114X)) of the [2XDigraphSymmetricClosure[102X
  ([14X3.3-12[114X) of [3Xdigraph[103X.[133X
  
  [33X[0;0YThe  set  of weakly connected components is a partition of the vertex set of
  [3Xdigraph[103X.[133X
  
  [33X[0;0YThe record [10Xwcc[110X has 2 components: [10Xcomps[110X and [10Xid[110X. The component [10Xcomps[110X is a list
  of  the  weakly  connected components of [3Xdigraph[103X (each of which is a list of
  vertices).  The  component [10Xid[110X is a list such that the vertex [10Xi[110X is an element
  of the weakly connected component [10Xcomps[id[i]][110X.[133X
  
  [33X[0;0YThe  method  used  in  this  function  has complexity [22XO(m+n)[122X, where [22Xm[122X is the
  number of edges and [22Xn[122X is the number of vertices in the digraph.[133X
  
  [33X[0;0Y[10XDigraphNrConnectedComponents([3Xdigraph[103X[10X)[110X    is    simply    a    shortcut   for
  [10XLength(DigraphConnectedComponents([3Xdigraph[103X[10X).comps)[110X, and is no more efficient.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xgr := Digraph([[2], [3, 1], []]);[127X[104X
    [4X[28X<immutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphConnectedComponents(gr);[127X[104X
    [4X[28Xrec( comps := [ [ 1, 2, 3 ] ], id := [ 1, 1, 1 ] )[128X[104X
    [4X[25Xgap>[125X [27Xgr := Digraph([[1], [1, 2], []]);[127X[104X
    [4X[28X<immutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphConnectedComponents(gr);[127X[104X
    [4X[28Xrec( comps := [ [ 1, 2 ], [ 3 ] ], id := [ 1, 1, 2 ] )[128X[104X
    [4X[25Xgap>[125X [27XDigraphNrConnectedComponents(gr);[127X[104X
    [4X[28X2[128X[104X
    [4X[25Xgap>[125X [27Xgr := EmptyDigraph(0);[127X[104X
    [4X[28X<immutable empty digraph with 0 vertices>[128X[104X
    [4X[25Xgap>[125X [27XDigraphConnectedComponents(gr);[127X[104X
    [4X[28Xrec( comps := [  ], id := [  ] )[128X[104X
    [4X[25Xgap>[125X [27XD := CycleDigraph(IsMutableDigraph, 2);[127X[104X
    [4X[28X<mutable digraph with 2 vertices, 2 edges>[128X[104X
    [4X[25Xgap>[125X [27XG := CycleDigraph(3);[127X[104X
    [4X[28X<immutable cycle digraph with 3 vertices>[128X[104X
    [4X[25Xgap>[125X [27XDigraphDisjointUnion(D, G);[127X[104X
    [4X[28X<mutable digraph with 5 vertices, 5 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphConnectedComponents(D);[127X[104X
    [4X[28Xrec( comps := [ [ 1, 2 ], [ 3, 4, 5 ] ], id := [ 1, 1, 2, 2, 2 ] )[128X[104X
  [4X[32X[104X
  
  [1X5.4-10 DigraphConnectedComponent[101X
  
  [33X[1;0Y[29X[2XDigraphConnectedComponent[102X( [3Xdigraph[103X, [3Xvertex[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10YA list of vertices.[133X
  
  [33X[0;0YIf  [3Xvertex[103X  is  a vertex in the digraph [3Xdigraph[103X, then this operation returns
  the connected component of [3Xvertex[103X in [3Xdigraph[103X. See [2XDigraphConnectedComponents[102X
  ([14X5.4-9[114X) for more information.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[3], [2], [1, 2], [4]]);[127X[104X
    [4X[28X<immutable digraph with 4 vertices, 5 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphConnectedComponent(D, 3);[127X[104X
    [4X[28X[ 1, 2, 3 ][128X[104X
    [4X[25Xgap>[125X [27XDigraphConnectedComponent(D, 2);[127X[104X
    [4X[28X[ 1, 2, 3 ][128X[104X
    [4X[25Xgap>[125X [27XDigraphConnectedComponent(D, 4);[127X[104X
    [4X[28X[ 4 ][128X[104X
  [4X[32X[104X
  
  [1X5.4-11 DigraphStronglyConnectedComponents[101X
  
  [33X[1;0Y[29X[2XDigraphStronglyConnectedComponents[102X( [3Xdigraph[103X ) [32X attribute[133X
  [33X[1;0Y[29X[2XDigraphNrStronglyConnectedComponents[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA record.[133X
  
  [33X[0;0YThis function returns the record [10Xscc[110X corresponding to the strongly connected
  components  of  the digraph [3Xdigraph[103X. Two vertices of [3Xdigraph[103X are in the same
  strongly connected component whenever they are equal, or there is a directed
  path from each vertex to the other. The set of strongly connected components
  is a partition of the vertex set of [3Xdigraph[103X.[133X
  
  [33X[0;0YThe record [10Xscc[110X has 2 components: [10Xcomps[110X and [10Xid[110X. The component [10Xcomps[110X is a list
  of  the strongly connected components of [3Xdigraph[103X (each of which is a list of
  vertices).  The  component [10Xid[110X is a list such that the vertex [10Xi[110X is an element
  of the strongly connected component [10Xcomps[id[i]][110X.[133X
  
  [33X[0;0YThe  method  used  in  this  function  is a non-recursive version of Gabow's
  Algorithm  [Gab00]  and has complexity [22XO(m+n)[122X where [22Xm[122X is the number of edges
  (counting  multiple  edges  as  one)  and [22Xn[122X is the number of vertices in the
  digraph.[133X
  
  [33X[0;0Y[10XDigraphNrStronglyConnectedComponents([3Xdigraph[103X[10X)[110X   is  simply  a  shortcut  for
  [10XLength(DigraphStronglyConnectedComponents([3Xdigraph[103X[10X).comps)[110X,  and  is  no more
  efficient.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xgr := Digraph([[2], [3, 1], []]);[127X[104X
    [4X[28X<immutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphStronglyConnectedComponents(gr);[127X[104X
    [4X[28Xrec( comps := [ [ 3 ], [ 1, 2 ] ], id := [ 2, 2, 1 ] )[128X[104X
    [4X[25Xgap>[125X [27XDigraphNrStronglyConnectedComponents(gr);[127X[104X
    [4X[28X2[128X[104X
    [4X[25Xgap>[125X [27XD := DigraphDisjointUnion(CycleDigraph(4), CycleDigraph(5));[127X[104X
    [4X[28X<immutable digraph with 9 vertices, 9 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphStronglyConnectedComponents(D);[127X[104X
    [4X[28Xrec( comps := [ [ 1, 2, 3, 4 ], [ 5, 6, 7, 8, 9 ] ], [128X[104X
    [4X[28X  id := [ 1, 1, 1, 1, 2, 2, 2, 2, 2 ] )[128X[104X
    [4X[25Xgap>[125X [27XDigraphNrStronglyConnectedComponents(D);[127X[104X
    [4X[28X2[128X[104X
    [4X[25Xgap>[125X [27XD := CycleDigraph(IsMutableDigraph, 2);[127X[104X
    [4X[28X<mutable digraph with 2 vertices, 2 edges>[128X[104X
    [4X[25Xgap>[125X [27XG := CycleDigraph(3);[127X[104X
    [4X[28X<immutable cycle digraph with 3 vertices>[128X[104X
    [4X[25Xgap>[125X [27XDigraphDisjointUnion(D, G);[127X[104X
    [4X[28X<mutable digraph with 5 vertices, 5 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphStronglyConnectedComponents(D);[127X[104X
    [4X[28Xrec( comps := [ [ 1, 2 ], [ 3, 4, 5 ] ], id := [ 1, 1, 2, 2, 2 ] )[128X[104X
  [4X[32X[104X
  
  [1X5.4-12 DigraphStronglyConnectedComponent[101X
  
  [33X[1;0Y[29X[2XDigraphStronglyConnectedComponent[102X( [3Xdigraph[103X, [3Xvertex[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10YA list of vertices.[133X
  
  [33X[0;0YIf  [3Xvertex[103X  is  a vertex in the digraph [3Xdigraph[103X, then this operation returns
  the    strongly    connected   component   of   [3Xvertex[103X   in   [3Xdigraph[103X.   See
  [2XDigraphStronglyConnectedComponents[102X ([14X5.4-11[114X) for more information.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[3], [2], [1, 2], [3]]);[127X[104X
    [4X[28X<immutable digraph with 4 vertices, 5 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphStronglyConnectedComponent(D, 3);[127X[104X
    [4X[28X[ 1, 3 ][128X[104X
    [4X[25Xgap>[125X [27XDigraphStronglyConnectedComponent(D, 2);[127X[104X
    [4X[28X[ 2 ][128X[104X
    [4X[25Xgap>[125X [27XDigraphStronglyConnectedComponent(D, 4);[127X[104X
    [4X[28X[ 4 ][128X[104X
  [4X[32X[104X
  
  [1X5.4-13 DigraphBicomponents[101X
  
  [33X[1;0Y[29X[2XDigraphBicomponents[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA pair of lists of vertices, or [9Xfail[109X.[133X
  
  [33X[0;0YIf  [3Xdigraph[103X  is a bipartite digraph, i.e. if it satisfies [2XIsBipartiteDigraph[102X
  ([14X6.2-3[114X), then [10XDigraphBicomponents[110X returns a pair of bicomponents of [3Xdigraph[103X.
  Otherwise, [10XDigraphBicomponents[110X returns [9Xfail[109X.[133X
  
  [33X[0;0YFor  a bipartite digraph, the vertices can be partitioned into two non-empty
  sets  such  that  the source and range of any edge are in distinct sets. The
  parts  of this partition are called [13Xbicomponents[113X of [3Xdigraph[103X. Equivalently, a
  pair  of  bicomponents  of  [3Xdigraph[103X  consists  of  the  color-classes  of  a
  2-coloring of [3Xdigraph[103X.[133X
  
  [33X[0;0YFor  a bipartite digraph with at least 3 vertices, there is a unique pair of
  bicomponents  of  bipartite  if  and  only  if the digraph is connected. See
  [2XIsConnectedDigraph[102X ([14X6.5-3[114X) for more information.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := CycleDigraph(3);[127X[104X
    [4X[28X<immutable cycle digraph with 3 vertices>[128X[104X
    [4X[25Xgap>[125X [27XDigraphBicomponents(D);[127X[104X
    [4X[28Xfail[128X[104X
    [4X[25Xgap>[125X [27XD := ChainDigraph(5);[127X[104X
    [4X[28X<immutable chain digraph with 5 vertices>[128X[104X
    [4X[25Xgap>[125X [27XDigraphBicomponents(D);[127X[104X
    [4X[28X[ [ 1, 3, 5 ], [ 2, 4 ] ][128X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[5], [1, 4], [5], [5], []]);[127X[104X
    [4X[28X<immutable digraph with 5 vertices, 5 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphBicomponents(D);[127X[104X
    [4X[28X[ [ 1, 3, 4 ], [ 2, 5 ] ][128X[104X
    [4X[25Xgap>[125X [27XD := CompleteBipartiteDigraph(IsMutableDigraph, 2, 3);[127X[104X
    [4X[28X<mutable digraph with 5 vertices, 12 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphBicomponents(D);[127X[104X
    [4X[28X[ [ 1, 2 ], [ 3, 4, 5 ] ][128X[104X
  [4X[32X[104X
  
  [1X5.4-14 ArticulationPoints[101X
  
  [33X[1;0Y[29X[2XArticulationPoints[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA list of vertices.[133X
  
  [33X[0;0YA connected digraph is [13Xbiconnected[113X if it is still connected (in the sense of
  [2XIsConnectedDigraph[102X  ([14X6.5-3[114X))  when  any  vertex  is  removed. If the digraph
  [3Xdigraph[103X  is  not  biconnected but is connected, then any vertex [10Xv[110X of [3Xdigraph[103X
  whose  removal  makes  the  resulting  digraph  disconnected  is  called  an
  [13Xarticulation point[113X.[133X
  
  [33X[0;0Y[10XArticulationPoints[110X  returns a list of the articulation points of [3Xdigraph[103X, if
  any, and, in particular, returns the empty list if [3Xdigraph[103X is not connected.[133X
  
  [33X[0;0YMultiple edges are ignored by this method.[133X
  
  [33X[0;0YThe  method  used  in  this  operation  has complexity [22XO(m+n)[122X where [22Xm[122X is the
  number of edges and [22Xn[122X is the number of vertices in the digraph.[133X
  
  [33X[0;0YIf [3XD[103X has a bridge (see [2XBridges[102X ([14X5.4-15[114X)), then a node incident to the bridge
  is an articulation point if and only if it has degree at least [22X2[122X. It follows
  that  if [3XD[103X has a bridge and at least [22X3[122X nodes, then at least one of the nodes
  incident to the bridge is an articulation point. The converse does not hold,
  there are digraphs with articulation points, but no bridges.[133X
  
  [33X[0;0YSee also [2XIsBiconnectedDigraph[102X ([14X6.5-4[114X) and [2XIsBridgelessDigraph[102X ([14X6.5-5[114X).[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XArticulationPoints(CycleDigraph(5));[127X[104X
    [4X[28X[  ][128X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[2, 7], [3, 5], [4], [2], [6], [1], []]);;[127X[104X
    [4X[25Xgap>[125X [27XArticulationPoints(D);[127X[104X
    [4X[28X[ 2, 1 ][128X[104X
    [4X[25Xgap>[125X [27XArticulationPoints(ChainDigraph(5));[127X[104X
    [4X[28X[ 4, 3, 2 ][128X[104X
    [4X[25Xgap>[125X [27XArticulationPoints(NullDigraph(5));[127X[104X
    [4X[28X[  ][128X[104X
    [4X[25Xgap>[125X [27XD := ChainDigraph(IsMutableDigraph, 4);[127X[104X
    [4X[28X<mutable digraph with 4 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XArticulationPoints(D);[127X[104X
    [4X[28X[ 3, 2 ][128X[104X
  [4X[32X[104X
  
  [1X5.4-15 Bridges[101X
  
  [33X[1;0Y[29X[2XBridges[102X( [3XD[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA (possibly empty) list of edges.[133X
  
  [33X[0;0YA  connected  digraph  is  [13X2-edge-connected[113X if it is still connected (in the
  sense  of  [2XIsConnectedDigraph[102X  ([14X6.5-3[114X))  when  any  edge  is removed. If the
  digraph  [3XD[103X is not 2-edge-connected but is connected, then any edge [10X[u, v][110X of
  [3XD[103X whose removal makes the resulting digraph disconnected is called a [13Xbridge[113X.[133X
  
  [33X[0;0Y[10XBridges[110X  returns  a  list  of  the bridges of [3XD[103X, if any, and, in particular,
  returns the empty list if [3XD[103X is not connected.[133X
  
  [33X[0;0YMultiple edges are ignored by this method.[133X
  
  [33X[0;0YThe  method  used  in  this  operation  has complexity [22XO(m+n)[122X where [22Xm[122X is the
  number of edges and [22Xn[122X is the number of vertices in the digraph.[133X
  
  [33X[0;0YIf  [3XD[103X  has  a  bridge, then a node incident to the bridge is an articulation
  point  (see  [2XArticulationPoints[102X  ([14X5.4-14[114X))  if  and only if it has degree at
  least  [22X2[122X.  It  follows  that if [3XD[103X has a bridge and at least [22X3[122X nodes, then at
  least  one of the nodes incident to the bridge is an articulation point. The
  converse  does not hold, there are digraphs with articulation points, but no
  bridges.[133X
  
  [33X[0;0YSee also [2XIsBiconnectedDigraph[102X ([14X6.5-4[114X) and [2XIsBridgelessDigraph[102X ([14X6.5-5[114X).[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[2, 5], [1, 3, 4, 5], [2, 4], [2, 3], [1, 2]]);[127X[104X
    [4X[28X<immutable digraph with 5 vertices, 12 edges>[128X[104X
    [4X[25Xgap>[125X [27XBridges(D);[127X[104X
    [4X[28X[  ][128X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[2], [3], [4], [2]]);[127X[104X
    [4X[28X<immutable digraph with 4 vertices, 4 edges>[128X[104X
    [4X[25Xgap>[125X [27XBridges(D);[127X[104X
    [4X[28X[ [ 1, 2 ] ][128X[104X
    [4X[25Xgap>[125X [27XBridges(ChainDigraph(2));[127X[104X
    [4X[28X[ [ 1, 2 ] ][128X[104X
    [4X[25Xgap>[125X [27XArticulationPoints(ChainDigraph(2));[127X[104X
    [4X[28X[  ][128X[104X
  [4X[32X[104X
  
  [1X5.4-16 StrongOrientation[101X
  
  [33X[1;0Y[29X[2XStrongOrientation[102X( [3XD[103X ) [32X operation[133X
  [33X[1;0Y[29X[2XStrongOrientationAttr[102X( [3XD[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA digraph or [9Xfail[109X.[133X
  
  [33X[0;0YA  [13Xstrong orientation[113X of a connected symmetric digraph [3XD[103X (if it exists) is a
  strongly  connected  subdigraph  [10XC[110X of [3XD[103X such that for every edge [10X[u, v][110X of [3XD[103X
  either  [10X[u,  v][110X  or  [10X[v,  u][110X  is an edge of [10XC[110X but not both. Robbin's Theorem
  states  that  a  digraph  admits  a  strong orientation if and only if it is
  bridgeless (see [2XIsBridgelessDigraph[102X ([14X6.5-5[114X)).[133X
  
  [33X[0;0YThis  operation  returns  a  strong  orientation  of  the  digraph [3XD[103X if [3XD[103X is
  symmetric  and [3XD[103X admits a strong orientation. If [3XD[103X is symmetric but does not
  admit  a  strong  orientation, then [9Xfail[109X is returned. If [3XD[103X is not symmetric,
  then an error is given.[133X
  
  [33X[0;0YIf [3XD[103X is immutable, [10XStrongOrientation([3XD[103X[10X)[110X returns an immutable digraph, and if
  [3XD[103X is mutable, then [10XStrongOrientation([3XD[103X[10X)[110X returns a mutable digraph.[133X
  
  [33X[0;0YThe  method  used  in  this  operation  has complexity [22XO(m+n)[122X where [22Xm[122X is the
  number of edges and [22Xn[122X is the number of vertices in the digraph.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XStrongOrientation(DigraphSymmetricClosure(CycleDigraph(5))) [127X[104X
    [4X[25X>[125X [27X= CycleDigraph(5);[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27XD := DigraphSymmetricClosure(Digraph([127X[104X
    [4X[25X>[125X [27X[[2, 7], [3, 5], [4], [2], [6], [1], []]));;[127X[104X
    [4X[25Xgap>[125X [27XIsBridgelessDigraph(D);[127X[104X
    [4X[28Xfalse[128X[104X
    [4X[25Xgap>[125X [27XStrongOrientation(D);[127X[104X
    [4X[28Xfail[128X[104X
    [4X[25Xgap>[125X [27XStrongOrientation(NullDigraph(0));[127X[104X
    [4X[28X<immutable empty digraph with 0 vertices>[128X[104X
    [4X[25Xgap>[125X [27XStrongOrientation(DigraphDisjointUnion(CompleteDigraph(3), [127X[104X
    [4X[25X>[125X [27X                                          CompleteDigraph(3)));[127X[104X
    [4X[28Xfail[128X[104X
  [4X[32X[104X
  
  [1X5.4-17 DigraphPeriod[101X
  
  [33X[1;0Y[29X[2XDigraphPeriod[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YAn integer.[133X
  
  [33X[0;0YThis function returns the period of the digraph [3Xdigraph[103X.[133X
  
  [33X[0;0YIf a digraph [3Xdigraph[103X has at least one directed cycle, then the period is the
  greatest  positive  integer which divides the lengths of all directed cycles
  of [3Xdigraph[103X. If [3Xdigraph[103X has no directed cycles, then this function returns [22X0[122X.
  See Section [14X1.1-1[114X for the definition of a directed cycle.[133X
  
  [33X[0;0YA digraph with a period of [22X1[122X is said to be [13Xaperiodic[113X. See [2XIsAperiodicDigraph[102X
  ([14X6.5-7[114X).[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[6], [1], [2], [3], [4, 4], [5]]);[127X[104X
    [4X[28X<immutable multidigraph with 6 vertices, 7 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphPeriod(D);[127X[104X
    [4X[28X6[128X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[2], [3, 5], [4], [5], [1, 2]]);[127X[104X
    [4X[28X<immutable digraph with 5 vertices, 7 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphPeriod(D);[127X[104X
    [4X[28X1[128X[104X
    [4X[25Xgap>[125X [27XD := ChainDigraph(2);[127X[104X
    [4X[28X<immutable chain digraph with 2 vertices>[128X[104X
    [4X[25Xgap>[125X [27XDigraphPeriod(D);[127X[104X
    [4X[28X0[128X[104X
    [4X[25Xgap>[125X [27XIsAcyclicDigraph(D);[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27XD := GeneralisedPetersenGraph(IsMutableDigraph, 5, 2);[127X[104X
    [4X[28X<mutable digraph with 10 vertices, 30 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphPeriod(D);[127X[104X
    [4X[28X1[128X[104X
  [4X[32X[104X
  
  [1X5.4-18 DigraphFloydWarshall[101X
  
  [33X[1;0Y[29X[2XDigraphFloydWarshall[102X( [3Xdigraph[103X, [3Xfunc[103X, [3Xnopath[103X, [3Xedge[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10YA matrix.[133X
  
  [33X[0;0YIf  [3Xdigraph[103X is a digraph with [22Xn[122X vertices, then this operation returns an [22Xn ×
  n[122X  matrix  [10Xmat[110X  containing  the  output  of  a  generalised  version  of the
  Floyd-Warshall algorithm, applied to [3Xdigraph[103X.[133X
  
  [33X[0;0YThe  operation  [10XDigraphFloydWarshall[110X  is  customised  by the arguments [3Xfunc[103X,
  [3Xnopath[103X,  and  [3Xedge[103X.  The  arguments  [3Xnopath[103X  and  [3Xedge[103X  can be arbitrary [5XGAP[105X
  objects. The argument [3Xfunc[103X must be a function which accepts 4 arguments: the
  matrix  [10Xmat[110X,  followed by 3 postive integers. The function [3Xfunc[103X is where the
  work to calculate the desired outcome must be performed.[133X
  
  [33X[0;0YThis  method  initialises the matrix [10Xmat[110X by setting entry [10Xmat[i][j][110X to equal
  [3Xedge[103X  if  there  is  an edge with source [10Xi[110X and range [10Xj[110X, and by setting entry
  [10Xmat[i][j][110X  to equal [3Xnopath[103X otherwise. The final part of [10XDigraphFloydWarshall[110X
  then  calls  the  function  [3Xfunc[103X  inside  three  nested  for loops, over the
  vertices of [3Xdigraph[103X:[133X
  
  [4X[32X[104X
    [4Xfor i in DigraphsVertices(digraph) do[104X
    [4X  for j in DigraphsVertices(digraph) do[104X
    [4X    for k in DigraphsVertices(digraph) do[104X
    [4X      func(mat, i, j, k);[104X
    [4X    od;[104X
    [4X  od;[104X
    [4Xod;[104X
  [4X[32X[104X
  
  [33X[0;0YThe  matrix  [10Xmat[110X  is  then  returned  as  the  result.  An  example of using
  [10XDigraphFloydWarshall[110X  to calculate the shortest (non-zero) distances between
  the vertices of a digraph is shown below:[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := DigraphFromDigraph6String("&EAHQeDB");[127X[104X
    [4X[28X<immutable digraph with 6 vertices, 12 edges>[128X[104X
    [4X[25Xgap>[125X [27Xfunc := function(mat, i, j, k)[127X[104X
    [4X[25X>[125X [27X  if mat[i][k] <> -1 and mat[k][j] <> -1 then[127X[104X
    [4X[25X>[125X [27X    if (mat[i][j] = -1) or (mat[i][j] > mat[i][k] + mat[k][j]) then[127X[104X
    [4X[25X>[125X [27X      mat[i][j] := mat[i][k] + mat[k][j];[127X[104X
    [4X[25X>[125X [27X    fi;[127X[104X
    [4X[25X>[125X [27X  fi;[127X[104X
    [4X[25X>[125X [27Xend;[127X[104X
    [4X[28Xfunction( mat, i, j, k ) ... end[128X[104X
    [4X[25Xgap>[125X [27Xshortest_distances := DigraphFloydWarshall(D, func, -1, 1);;[127X[104X
    [4X[25Xgap>[125X [27XDisplay(shortest_distances);[127X[104X
    [4X[28X[ [   3,  -1,  -1,   2,   1,   2 ],[128X[104X
    [4X[28X  [   4,   2,   1,   3,   2,   1 ],[128X[104X
    [4X[28X  [   3,   1,   2,   2,   1,   2 ],[128X[104X
    [4X[28X  [   1,  -1,  -1,   1,   1,   2 ],[128X[104X
    [4X[28X  [   2,  -1,  -1,   1,   2,   1 ],[128X[104X
    [4X[28X  [   3,  -1,  -1,   2,   1,   1 ] ][128X[104X
  [4X[32X[104X
  
  [1X5.4-19 IsReachable[101X
  
  [33X[1;0Y[29X[2XIsReachable[102X( [3Xdigraph[103X, [3Xu[103X, [3Xv[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10Y[9Xtrue[109X or [9Xfalse[109X.[133X
  
  [33X[0;0YThis operation returns [9Xtrue[109X if there exists a non-trivial directed walk from
  vertex  [3Xu[103X  to  vertex  [3Xv[103X in the digraph [3Xdigraph[103X, and [9Xfalse[109X if there does not
  exist  such  a  directed  walk.  See  Section  [14X1.1-1[114X for the definition of a
  non-trivial directed walk.[133X
  
  [33X[0;0YThe  method for [10XIsReachable[110X has worst case complexity of [22XO(m + n)[122X where [22Xm[122X is
  the number of edges and [22Xn[122X the number of vertices in [3Xdigraph[103X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[2], [3], [2, 3]]);[127X[104X
    [4X[28X<immutable digraph with 3 vertices, 4 edges>[128X[104X
    [4X[25Xgap>[125X [27XIsReachable(D, 1, 3);[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27XIsReachable(D, 2, 1);[127X[104X
    [4X[28Xfalse[128X[104X
    [4X[25Xgap>[125X [27XIsReachable(D, 3, 3);[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27XIsReachable(D, 1, 1);[127X[104X
    [4X[28Xfalse[128X[104X
  [4X[32X[104X
  
  [1X5.4-20 IsDigraphPath[101X
  
  [33X[1;0Y[29X[2XIsDigraphPath[102X( [3XD[103X, [3Xv[103X, [3Xa[103X ) [32X operation[133X
  [33X[1;0Y[29X[2XIsDigraphPath[102X( [3XD[103X, [3Xlist[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10Y[9Xtrue[109X or [9Xfalse[109X.[133X
  
  [33X[0;0YThis  function returns [9Xtrue[109X if the arguments [3Xv[103X and [3Xa [103X describe a path in the
  digraph [3XD[103X. A directed path (or directed cycle) of non-zero length [10Xn-1[110X, [22X(v_1,
  e_1, v_2, e_2, ..., e_n-1, v_n)[122X, is represented by a pair of lists [10X[[3Xv[103X[10X, [3Xa[103X[10X][110X as
  follows:[133X
  
  [30X    [33X[0;6Y[3Xv[103X is the list [22X[v_1, v_2, ..., v_n][122X.[133X
  
  [30X    [33X[0;6Y[3Xa[103X  is  the  list of positive integers [22X[a_1, a_2, ..., a_n-1][122X where for
        each   each   [22Xi   <   n[122X,   [22Xa_i[122X   is   the   position   of   [22Xv_i+1[122X   in
        [10XOutNeighboursOfVertex([110X[3XD[103X[10X,[110X[22Xv_i[122X[10X)[110X  corresponding  to the edge [22Xe_i[122X. This can
        be  useful  if  the position of a vertex in a list of out-neighours is
        significant, for example in orbit digraphs.[133X
  
  [33X[0;0YIf  the  arguments to [10XIsDigraphPath[110X are a digraph [3XD[103X and list [3Xlist[103X, then this
  is equivalent to calling [10XIsDigraphPath([3XD[103X[10X, [3Xlist[103X[10X[1], [3Xlist[103X[10X[2])[110X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph(IsMutableDigraph, Combinations([1 .. 5]), IsSubset);[127X[104X
    [4X[28X<mutable digraph with 32 vertices, 243 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphReflexiveTransitiveReduction(D);[127X[104X
    [4X[28X<mutable digraph with 32 vertices, 80 edges>[128X[104X
    [4X[25Xgap>[125X [27XMakeImmutable(D);[127X[104X
    [4X[28X<immutable digraph with 32 vertices, 80 edges>[128X[104X
    [4X[25Xgap>[125X [27XIsDigraphPath(D, [32, 31, 33], [1, 1]);[127X[104X
    [4X[28Xfalse[128X[104X
    [4X[25Xgap>[125X [27XIsDigraphPath(D, [1], []);[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27XIsDigraphPath(D, [6, 9, 16, 17], [3, 3, 2]);[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27XIsDigraphPath(D, DigraphPath(D, 6, 1));[127X[104X
    [4X[28Xtrue[128X[104X
  [4X[32X[104X
  
  [1X5.4-21 VerticesReachableFrom[101X
  
  [33X[1;0Y[29X[2XVerticesReachableFrom[102X( [3Xdigraph[103X, [3Xroot[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10YA list.[133X
  
  [33X[0;0YThis  operation  returns  a list of the vertices [3Xv[103X, for which there exists a
  non-trivial  directed  walk  from  vertex  [3Xroot[103X  to  vertex [3Xv[103X in the digraph
  [3Xdigraph[103X.  See  Section  [14X1.1-1[114X  for  the definition of a non-trivial directed
  walk.[133X
  
  [33X[0;0YThe  method  for [10XVerticesReachableFrom[110X has worst case complexity of [22XO(m + n)[122X
  where [22Xm[122X is the number of edges and [22Xn[122X the number of vertices in [3Xdigraph[103X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := CompleteDigraph(5);[127X[104X
    [4X[28X<immutable complete digraph with 5 vertices>[128X[104X
    [4X[25Xgap>[125X [27XVerticesReachableFrom(D, 1);[127X[104X
    [4X[28X[ 2, 1, 3, 4, 5 ][128X[104X
    [4X[25Xgap>[125X [27XVerticesReachableFrom(D, 3);[127X[104X
    [4X[28X[ 1, 2, 3, 4, 5 ][128X[104X
    [4X[25Xgap>[125X [27XD := EmptyDigraph(5);[127X[104X
    [4X[28X<immutable empty digraph with 5 vertices>[128X[104X
    [4X[25Xgap>[125X [27XVerticesReachableFrom(D, 1);[127X[104X
    [4X[28X[  ][128X[104X
    [4X[25Xgap>[125X [27XVerticesReachableFrom(D, 3);[127X[104X
    [4X[28X[  ][128X[104X
    [4X[25Xgap>[125X [27XD := CycleDigraph(4);[127X[104X
    [4X[28X<immutable cycle digraph with 4 vertices>[128X[104X
    [4X[25Xgap>[125X [27XVerticesReachableFrom(D, 1);[127X[104X
    [4X[28X[ 2, 3, 4, 1 ][128X[104X
    [4X[25Xgap>[125X [27XVerticesReachableFrom(D, 3);[127X[104X
    [4X[28X[ 4, 1, 2, 3 ][128X[104X
    [4X[25Xgap>[125X [27XD := ChainDigraph(5);[127X[104X
    [4X[28X<immutable chain digraph with 5 vertices>[128X[104X
    [4X[25Xgap>[125X [27XVerticesReachableFrom(D, 1);[127X[104X
    [4X[28X[ 2, 3, 4, 5 ][128X[104X
    [4X[25Xgap>[125X [27XVerticesReachableFrom(D, 3);[127X[104X
    [4X[28X[ 4, 5 ][128X[104X
    [4X[25Xgap>[125X [27XVerticesReachableFrom(D, 5);[127X[104X
    [4X[28X[  ][128X[104X
  [4X[32X[104X
  
  [1X5.4-22 DigraphPath[101X
  
  [33X[1;0Y[29X[2XDigraphPath[102X( [3Xdigraph[103X, [3Xu[103X, [3Xv[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10YA pair of lists, or [9Xfail[109X.[133X
  
  [33X[0;0YIf  there exists a non-trivial directed path (or a non-trivial cycle, in the
  case that [3Xu[103X [10X=[110X [3Xv[103X) from vertex [3Xu[103X to vertex [3Xv[103X in the digraph [3Xdigraph[103X, then this
  operation  returns such a directed path (or directed cycle). Otherwise, this
  operation  returns  [9Xfail[109X.  See Section [14X'[33X[0;0YDefinitions[133X'[114X for the definition of a
  directed path and a directed cycle.[133X
  
  [33X[0;0YA  directed path (or directed cycle) of non-zero length [10Xn-1[110X, [22X(v_1, e_1, v_2,
  e_2, ..., e_n-1, v_n)[122X, is represented by a pair of lists [10X[v,a][110X as follows:[133X
  
  [30X    [33X[0;6Y[10Xv[110X is the list [22X[v_1, v_2, ..., v_n][122X.[133X
  
  [30X    [33X[0;6Y[10Xa[110X  is  the  list of positive integers [22X[a_1, a_2, ..., a_n-1][122X where for
        each   each   [22Xi   <   n[122X,   [22Xa_i[122X   is   the   position   of   [22Xv_i+1[122X   in
        [10XOutNeighboursOfVertex([110X[3Xdigraph[103X[10X,[110X[22Xv_i[122X[10X)[110X corresponding to the edge [22Xe_i[122X. This
        can  be  useful if the position of a vertex in a list of out-neighours
        is significant, for example in orbit digraphs.[133X
  
  [33X[0;0YThe  method for [10XDigraphPath[110X has worst case complexity of [22XO(m + n)[122X where [22Xm[122X is
  the number of edges and [22Xn[122X the number of vertices in [3Xdigraph[103X.[133X
  
  [33X[0;0YSee also [2XIsDigraphPath[102X ([14X5.4-20[114X).[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[2], [3], [2, 3]]);[127X[104X
    [4X[28X<immutable digraph with 3 vertices, 4 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphPath(D, 1, 3);[127X[104X
    [4X[28X[ [ 1, 2, 3 ], [ 1, 1 ] ][128X[104X
    [4X[25Xgap>[125X [27XDigraphPath(D, 2, 1);[127X[104X
    [4X[28Xfail[128X[104X
    [4X[25Xgap>[125X [27XDigraphPath(D, 3, 3);[127X[104X
    [4X[28X[ [ 3, 3 ], [ 2 ] ][128X[104X
    [4X[25Xgap>[125X [27XDigraphPath(D, 1, 1);[127X[104X
    [4X[28Xfail[128X[104X
  [4X[32X[104X
  
  [1X5.4-23 DigraphShortestPath[101X
  
  [33X[1;0Y[29X[2XDigraphShortestPath[102X( [3Xdigraph[103X, [3Xu[103X, [3Xv[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10YA pair of lists, or [9Xfail[109X.[133X
  
  [33X[0;0YReturns  a  shortest  directed  path in the digraph [3Xdigraph[103X from vertex [3Xu[103X to
  vertex  [3Xv[103X,  if  such  a path exists. If [10X[3Xu[103X[10X = [3Xv[103X[10X[110X, then the shortest non-trivial
  cycle  is  returned,  again, if it exists. Otherwise, this operation returns
  [9Xfail[109X.  See Section [14X'[33X[0;0YDefinitions[133X'[114X for the definition of a directed path and a
  directed cycle.[133X
  
  [33X[0;0YSee  [2XDigraphPath[102X  ([14X5.4-22[114X)  for  details  on  the  output.  The  method  for
  [10XDigraphShortestPath[110X  has  worst  case  complexity of [22XO(m + n)[122X where [22Xm[122X is the
  number of edges and [22Xn[122X the number of vertices in [3Xdigraph[103X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[1, 2], [3], [2, 4], [1], [2, 4]]);[127X[104X
    [4X[28X<immutable digraph with 5 vertices, 8 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphShortestPath(D, 5, 1);[127X[104X
    [4X[28X[ [ 5, 4, 1 ], [ 2, 1 ] ][128X[104X
    [4X[25Xgap>[125X [27XDigraphShortestPath(D, 3, 3);[127X[104X
    [4X[28X[ [ 3, 2, 3 ], [ 1, 1 ] ][128X[104X
    [4X[25Xgap>[125X [27XDigraphShortestPath(D, 5, 5);[127X[104X
    [4X[28Xfail[128X[104X
    [4X[25Xgap>[125X [27XDigraphShortestPath(D, 1, 1);[127X[104X
    [4X[28X[ [ 1, 1 ], [ 1 ] ][128X[104X
  [4X[32X[104X
  
  [1X5.4-24 DigraphRandomWalk[101X
  
  [33X[1;0Y[29X[2XDigraphRandomWalk[102X( [3Xdigraph[103X, [3Xv[103X, [3Xt[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10YA pair of lists.[133X
  
  [33X[0;0YReturns  a  directed  path  corresponding  to  a  [13Xrandom walk[113X in the digraph
  [3Xdigraph[103X, starting at vertex [3Xv[103X and having length no more than [3Xt[103X.[133X
  
  [33X[0;0YA  random walk is defined as follows. The path begins at [3Xv[103X, and at each step
  it  follows  a  random edge leaving the current vertex. It continues through
  the  digraph in this way until it has traversed [3Xt[103X edges, or until it reaches
  a vertex with no out-edges (a [13Xsink[113X) and therefore cannot continue.[133X
  
  [33X[0;0YThe output has the same form as that of [2XDigraphPath[102X ([14X5.4-22[114X).[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[1, 2], [3], [2, 4], [1], [2, 4]]);                [127X[104X
    [4X[28X<immutable digraph with 5 vertices, 8 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphRandomWalk(D, 1, 4);[127X[104X
    [4X[28X[ [ 1, 2, 3, 2, 3 ], [ 2, 1, 1, 1 ] ][128X[104X
  [4X[32X[104X
  
  [1X5.4-25 Dominators[101X
  
  [33X[1;0Y[29X[2XDominators[102X( [3Xdigraph[103X, [3Xroot[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10YA list of lists.[133X
  
  [33X[0;0Y[10XDominators[110X  takes  a  [3Xdigraph[103X  and a root [3Xroot[103X and returns the dominators of
  each  vertex  with  respect to the root. The output is returned as a list of
  length  [10XDigraphNrVertices([3XDigraph[103X[10X)[110X,  whose  [3Xi[103Xth  entry  is  a  list with the
  dominators  of vertex [3Xi[103X of the [3Xdigraph[103X. If there is no path from the root to
  a  specific  vertex,  the  output  will  contain a hole in the corresponding
  position.  The  [13Xdominators[113X of a vertex [22Xu[122X are the vertices that are contained
  in  every  path  from  the [22Xroot[122X to [22Xu[122X, not including [22Xu[122X itself. The method for
  this  operation  is an implementation of an algorithm by Thomas Lengauer and
  Robert  Endre  Tarjan  [LT79]. The complexity of this algorithm is [22XO(mlog n)[122X
  where  [22Xm[122X  is  the  number  of  edges  and  [22Xn[122X  is  the number of nodes in the
  subdigraph induced by the nodes in [3Xdigraph[103X reachable from [3Xroot[103X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[2], [3, 6], [2, 4], [1], [], [3]]);[127X[104X
    [4X[28X<immutable digraph with 6 vertices, 7 edges>[128X[104X
    [4X[25Xgap>[125X [27XDominators(D, 1);[127X[104X
    [4X[28X[ , [ 1 ], [ 2, 1 ], [ 3, 2, 1 ],, [ 2, 1 ] ][128X[104X
    [4X[25Xgap>[125X [27XDominators(D, 2);[127X[104X
    [4X[28X[ [ 4, 3, 2 ],, [ 2 ], [ 3, 2 ],, [ 2 ] ][128X[104X
    [4X[25Xgap>[125X [27XDominators(D, 3);[127X[104X
    [4X[28X[ [ 4, 3 ], [ 3 ],, [ 3 ],, [ 2, 3 ] ][128X[104X
    [4X[25Xgap>[125X [27XDominators(D, 4);[127X[104X
    [4X[28X[ [ 4 ], [ 1, 4 ], [ 2, 1, 4 ],,, [ 2, 1, 4 ] ][128X[104X
    [4X[25Xgap>[125X [27XDominators(D, 5);[127X[104X
    [4X[28X[  ][128X[104X
    [4X[25Xgap>[125X [27XDominators(D, 6);[127X[104X
    [4X[28X[ [ 4, 3, 6 ], [ 3, 6 ], [ 6 ], [ 3, 6 ] ][128X[104X
  [4X[32X[104X
  
  [1X5.4-26 DominatorTree[101X
  
  [33X[1;0Y[29X[2XDominatorTree[102X( [3Xdigraph[103X, [3Xroot[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10YA record.[133X
  
  [33X[0;0Y[10XDominatorTree[110X  takes  a  [3Xdigraph[103X and a [3Xroot[103X vertex and returns a record with
  the following components:[133X
  
  [8Xidom[108X
        [33X[0;6Ythe immediate dominators of the vertices with respect to the root.[133X
  
  [8Xpreorder[108X
        [33X[0;6Ythe  preorder values of the vertices defined by the depth first search
        executed on the digraph.[133X
  
  [33X[0;0YThe  [13Ximmediate  dominator[113X of a vertex [22Xu[122X is the unique dominator of [22Xu[122X that is
  dominated  by  all other dominators of [22Xu[122X. The algorithm is an implementation
  of  the  fast  algorithm  written by Thomas Lengauer and Robert Endre Tarjan
  [LT79].  The complexity of this algorithm is [22XO(mlog n)[122X where [22Xm[122X is the number
  of edges and [22Xn[122X is the number of nodes in the subdigraph induced by the nodes
  in [3Xdigraph[103X reachable from [3Xroot[103X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[2, 3], [4, 6], [4, 5], [3, 5], [1, 6], [2, 3]]);[127X[104X
    [4X[28X<immutable digraph with 6 vertices, 12 edges>[128X[104X
    [4X[25Xgap>[125X [27XDominatorTree(D, 1);[127X[104X
    [4X[28Xrec( idom := [ fail, 1, 1, 1, 1, 1 ], [128X[104X
    [4X[28X  preorder := [ 1, 2, 4, 3, 5, 6 ] )[128X[104X
    [4X[25Xgap>[125X [27XDominatorTree(D, 5);[127X[104X
    [4X[28Xrec( idom := [ 5, 5, 5, 5, fail, 5 ], [128X[104X
    [4X[28X  preorder := [ 5, 1, 2, 4, 3, 6 ] )[128X[104X
    [4X[25Xgap>[125X [27XD := CompleteDigraph(5);[127X[104X
    [4X[28X<immutable complete digraph with 5 vertices>[128X[104X
    [4X[25Xgap>[125X [27XDominatorTree(D, 1);[127X[104X
    [4X[28Xrec( idom := [ fail, 1, 1, 1, 1 ], preorder := [ 1, 2, 3, 4, 5 ] )[128X[104X
    [4X[25Xgap>[125X [27XDominatorTree(D, 2);[127X[104X
    [4X[28Xrec( idom := [ 2, fail, 2, 2, 2 ], preorder := [ 2, 1, 3, 4, 5 ] )[128X[104X
  [4X[32X[104X
  
  [1X5.4-27 IteratorOfPaths[101X
  
  [33X[1;0Y[29X[2XIteratorOfPaths[102X( [3Xdigraph[103X, [3Xu[103X, [3Xv[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10YAn iterator.[133X
  
  [33X[0;0YIf  [3Xdigraph[103X  is a digraph or a list of adjacencies which defines a digraph -
  see  [2XOutNeighbours[102X  ([14X5.2-6[114X) - then this operation returns an iterator of the
  non-trivial  directed  paths (or directed cycles, in the case that [3Xu[103X [10X=[110X [3Xv[103X) in
  [3Xdigraph[103X from the vertex [3Xu[103X to the vertex [3Xv[103X.[133X
  
  [33X[0;0YSee  [2XDigraphPath[102X  ([14X5.4-22[114X) for more information about the repesentation of a
  directed  path  or  directed  cycle  which  is  used,  and  see  [14X'Reference:
  Iterators'[114X  for  more information about iterators. See Section [14X'[33X[0;0YDefinitions[133X'[114X
  for the definition of a directed path and a directed cycle.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[1, 4, 4, 2], [3, 5], [2, 3], [1, 2], [4]]);[127X[104X
    [4X[28X<immutable multidigraph with 5 vertices, 11 edges>[128X[104X
    [4X[25Xgap>[125X [27Xiter := IteratorOfPaths(D, 1, 4);[127X[104X
    [4X[28X<iterator>[128X[104X
    [4X[25Xgap>[125X [27XNextIterator(iter);[127X[104X
    [4X[28X[ [ 1, 4 ], [ 2 ] ][128X[104X
    [4X[25Xgap>[125X [27XNextIterator(iter);[127X[104X
    [4X[28X[ [ 1, 4 ], [ 3 ] ][128X[104X
    [4X[25Xgap>[125X [27XNextIterator(iter);[127X[104X
    [4X[28X[ [ 1, 2, 5, 4 ], [ 4, 2, 1 ] ][128X[104X
    [4X[25Xgap>[125X [27XIsDoneIterator(iter);[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27Xiter := IteratorOfPaths(D, 4, 3);[127X[104X
    [4X[28X<iterator>[128X[104X
    [4X[25Xgap>[125X [27XNextIterator(iter);[127X[104X
    [4X[28X[ [ 4, 1, 2, 3 ], [ 1, 4, 1 ] ][128X[104X
  [4X[32X[104X
  
  [1X5.4-28 DigraphAllSimpleCircuits[101X
  
  [33X[1;0Y[29X[2XDigraphAllSimpleCircuits[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA list of lists of vertices.[133X
  
  [33X[0;0YIf [3Xdigraph[103X is a digraph, then [10XDigraphAllSimpleCircuits[110X returns a list of the
  [13Xsimple circuits[113X in [3Xdigraph[103X.[133X
  
  [33X[0;0YSee  Section  [14X1.1-1[114X  for  the  definition  of  a simple circuit, and related
  notions. Note that a loop is a simple circuit.[133X
  
  [33X[0;0YFor  a  digraph  without  multiple  edges,  a  simple  circuit  is  uniquely
  determined  by its subsequence of vertices. However this is not the case for
  a  multidigraph.  The  attribute  [10XDigraphAllSimpleCircuits[110X  ignores multiple
  edges,  and  identifies  a  simple  circuit  using  only  its subsequence of
  vertices. For example, although the simple circuits [22X(v, e, v)[122X and [22X(v, e', v)[122X
  (for    distinct    edges   [22Xe[122X   and   [22Xe'[122X)   are   mathematically   distinct,
  [10XDigraphAllSimpleCircuits[110X considers them to be the same.[133X
  
  [33X[0;0YWith  this  approach,  a directed circuit of length [10Xn[110X can be determined by a
  list  of  its  first  [10Xn[110X vertices. Thus a simple circuit [22X(v_1, e_1, v_2, e_2,
  ..., e_n-1, v_n, e_n+1, v_1)[122X can be represented as the list [22X[v_1, ..., v_n][122X,
  or  any  cyclic  permutation  thereof.  For  each simple circuit of [3Xdigraph[103X,
  [10XDigraphAllSimpleCircuits([3Xdigraph[103X[10X)[110X   includes  precisely  one  such  list  to
  represent the circuit.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[], [3], [2, 4], [5, 4], [4]]);[127X[104X
    [4X[28X<immutable digraph with 5 vertices, 6 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphAllSimpleCircuits(D);[127X[104X
    [4X[28X[ [ 4 ], [ 4, 5 ], [ 2, 3 ] ][128X[104X
    [4X[25Xgap>[125X [27XD := ChainDigraph(10);;[127X[104X
    [4X[25Xgap>[125X [27XDigraphAllSimpleCircuits(D);[127X[104X
    [4X[28X[  ][128X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[3], [1], [1]]);[127X[104X
    [4X[28X<immutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphAllSimpleCircuits(D);[127X[104X
    [4X[28X[ [ 1, 3 ] ][128X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[1, 1]]);[127X[104X
    [4X[28X<immutable multidigraph with 1 vertex, 2 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphAllSimpleCircuits(D);[127X[104X
    [4X[28X[ [ 1 ] ][128X[104X
    [4X[25Xgap>[125X [27XD := CycleDigraph(IsMutableDigraph, 3);[127X[104X
    [4X[28X<mutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphAllSimpleCircuits(D);[127X[104X
    [4X[28X[ [ 1, 2, 3 ] ][128X[104X
  [4X[32X[104X
  
  [1X5.4-29 DigraphLongestSimpleCircuit[101X
  
  [33X[1;0Y[29X[2XDigraphLongestSimpleCircuit[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA list of vertices, or [9Xfail[109X.[133X
  
  [33X[0;0YIf  [3Xdigraph[103X  is  a  digraph,  then  [10XDigraphLongestSimpleCircuit[110X  returns the
  longest  [13Xsimple  circuit[113X in [3Xdigraph[103X. See Section [14X1.1-1[114X for the definition of
  simple circuit, and the definition of length for a simple circuit.[133X
  
  [33X[0;0YThis  attribute  computes  [10XDigraphAllSimpleCircuits([110X[3Xdigraph[103X[10X)[110X to find all the
  simple  circuits  of  [3Xdigraph[103X,  and  returns one of maximal length. A simple
  circuit  is  represented as a list of vertices, in the same way as described
  in [2XDigraphAllSimpleCircuits[102X ([14X5.4-28[114X).[133X
  
  [33X[0;0YIf  [3Xdigraph[103X  has  no  simple  circuits, then this attribute returns [9Xfail[109X. If
  [3Xdigraph[103X  has multiple simple circuits of maximal length, then this attribute
  returns one of them.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[], [3], [2, 4], [5, 4], [4]]);;[127X[104X
    [4X[25Xgap>[125X [27XDigraphLongestSimpleCircuit(D);[127X[104X
    [4X[28X[ 4, 5 ][128X[104X
    [4X[25Xgap>[125X [27XD := ChainDigraph(10);;[127X[104X
    [4X[25Xgap>[125X [27XDigraphLongestSimpleCircuit(D);[127X[104X
    [4X[28Xfail[128X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[3], [1], [1, 4], [1, 1]]);;[127X[104X
    [4X[25Xgap>[125X [27XDigraphLongestSimpleCircuit(D);[127X[104X
    [4X[28X[ 1, 3, 4 ][128X[104X
    [4X[25Xgap>[125X [27XD := GeneralisedPetersenGraph(IsMutableDigraph, 4, 1);[127X[104X
    [4X[28X<mutable digraph with 8 vertices, 24 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphLongestSimpleCircuit(D);[127X[104X
    [4X[28X[ 1, 2, 3, 4, 8, 7, 6, 5 ][128X[104X
  [4X[32X[104X
  
  [1X5.4-30 DigraphLayers[101X
  
  [33X[1;0Y[29X[2XDigraphLayers[102X( [3Xdigraph[103X, [3Xvertex[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10YA list.[133X
  
  [33X[0;0YThis operation returns a list [9Xlist[109X such that [9Xlist[i][109X is the list of vertices
  whose  minimum  distance  from the vertex [3Xvertex[103X in [3Xdigraph[103X is [9Xi - 1[109X. Vertex
  [3Xvertex[103X is assumed to be at distance [9X0[109X from itself.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := CompleteDigraph(4);;[127X[104X
    [4X[25Xgap>[125X [27XDigraphLayers(D, 1);[127X[104X
    [4X[28X[ [ 1 ], [ 2, 3, 4 ] ][128X[104X
  [4X[32X[104X
  
  [1X5.4-31 DigraphDegeneracy[101X
  
  [33X[1;0Y[29X[2XDigraphDegeneracy[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA non-negative integer, or [9Xfail[109X.[133X
  
  [33X[0;0YIf   [3Xdigraph[103X   is   a   symmetric  digraph  without  multiple  edges  -  see
  [2XIsSymmetricDigraph[102X   ([14X6.2-14[114X)   and  [2XIsMultiDigraph[102X  ([14X6.2-11[114X)  -  then  this
  attribute returns the degeneracy of [3Xdigraph[103X.[133X
  
  [33X[0;0YThe  degeneracy  of a digraph is the least integer [10Xk[110X such that every induced
  of  [3Xdigraph[103X  contains a vertex whose number of neighbours (excluding itself)
  is at most [10Xk[110X. Note that this means that loops are ignored.[133X
  
  [33X[0;0YIf  [3Xdigraph[103X  is  not  symmetric  or  has  multiple edges then this attribute
  returns [9Xfail[109X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := DigraphSymmetricClosure(ChainDigraph(5));;[127X[104X
    [4X[25Xgap>[125X [27XDigraphDegeneracy(D);[127X[104X
    [4X[28X1[128X[104X
    [4X[25Xgap>[125X [27XD := CompleteDigraph(5);;[127X[104X
    [4X[25Xgap>[125X [27XDigraphDegeneracy(D);[127X[104X
    [4X[28X4[128X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[1], [2, 4, 5], [3, 4], [2, 3, 4], [2], []]);[127X[104X
    [4X[28X<immutable digraph with 6 vertices, 10 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphDegeneracy(D);[127X[104X
    [4X[28X1[128X[104X
    [4X[25Xgap>[125X [27XD := GeneralisedPetersenGraph(IsMutableDigraph, 10, 3);[127X[104X
    [4X[28X<mutable digraph with 20 vertices, 60 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphDegeneracy(D);[127X[104X
    [4X[28X3[128X[104X
  [4X[32X[104X
  
  [1X5.4-32 DigraphDegeneracyOrdering[101X
  
  [33X[1;0Y[29X[2XDigraphDegeneracyOrdering[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA list of integers, or [9Xfail[109X.[133X
  
  [33X[0;0YIf   [3Xdigraph[103X   is  a  digraph  for  which  [10XDigraphDegeneracy([110X[3Xdigraph[103X[10X)[110X  is  a
  non-negative  integer  [10Xk[110X  -  see  [2XDigraphDegeneracy[102X  ([14X5.4-31[114X)  -  then  this
  attribute  returns  a degeneracy ordering of the vertices of the vertices of
  [3Xdigraph[103X.[133X
  
  [33X[0;0YA  degeneracy  ordering  of  [3Xdigraph[103X  is  a list [10Xordering[110X of the vertices of
  [3Xdigraph[103X  ordered  such  that  for  any  position  [10Xi[110X  of the list, the vertex
  [10Xordering[i][110X has at most [10Xk[110X neighbours in later position of the list.[133X
  
  [33X[0;0YIf  [10XDigraphDegeneracy([110X[3Xdigraph[103X[10X)[110X  returns  [9Xfail[109X,  then  this attribute returns
  [9Xfail[109X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := DigraphSymmetricClosure(ChainDigraph(5));;[127X[104X
    [4X[25Xgap>[125X [27XDigraphDegeneracyOrdering(D);[127X[104X
    [4X[28X[ 5, 4, 3, 2, 1 ][128X[104X
    [4X[25Xgap>[125X [27XD := CompleteDigraph(5);;[127X[104X
    [4X[25Xgap>[125X [27XDigraphDegeneracyOrdering(D);[127X[104X
    [4X[28X[ 5, 4, 3, 2, 1 ][128X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[1], [2, 4, 5], [3, 4], [2, 3, 4], [2], []]);[127X[104X
    [4X[28X<immutable digraph with 6 vertices, 10 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphDegeneracyOrdering(D);[127X[104X
    [4X[28X[ 1, 6, 5, 2, 4, 3 ][128X[104X
    [4X[25Xgap>[125X [27XD := GeneralisedPetersenGraph(IsMutableDigraph, 3, 1);[127X[104X
    [4X[28X<mutable digraph with 6 vertices, 18 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphDegeneracyOrdering(D);[127X[104X
    [4X[28X[ 6, 5, 4, 1, 3, 2 ][128X[104X
  [4X[32X[104X
  
  [1X5.4-33 HamiltonianPath[101X
  
  [33X[1;0Y[29X[2XHamiltonianPath[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA list or [9Xfail[109X.[133X
  
  [33X[0;0YReturns a Hamiltonian path if one exists, [9Xfail[109X if not.[133X
  
  [33X[0;0YA  [13XHamiltonian path[113X of a digraph with [10Xn[110X vertices is directed cycle of length
  [10Xn[110X.  If  [3Xdigraph[103X  is  a  digraph  that contains a Hamiltonian path, then this
  function returns one, described in the form used by [2XDigraphAllSimpleCircuits[102X
  ([14X5.4-28[114X).  Note if [3Xdigraph[103X has 0 or 1 vertices, then [10XHamiltonianPath[110X returns
  [10X[][110X or [10X[1][110X, respectively.[133X
  
  [33X[0;0YThe  method  used  in  this  attribute has the same worst case complexity as
  [2XDigraphMonomorphism[102X ([14X7.3-4[114X).[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[]]);[127X[104X
    [4X[28X<immutable empty digraph with 1 vertex>[128X[104X
    [4X[25Xgap>[125X [27XHamiltonianPath(D);[127X[104X
    [4X[28X[ 1 ][128X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[2], [1]]);[127X[104X
    [4X[28X<immutable digraph with 2 vertices, 2 edges>[128X[104X
    [4X[25Xgap>[125X [27XHamiltonianPath(D);[127X[104X
    [4X[28X[ 1, 2 ][128X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[3], [], [2]]);[127X[104X
    [4X[28X<immutable digraph with 3 vertices, 2 edges>[128X[104X
    [4X[25Xgap>[125X [27XHamiltonianPath(D);[127X[104X
    [4X[28Xfail[128X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[2], [3], [1]]);[127X[104X
    [4X[28X<immutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XHamiltonianPath(D);[127X[104X
    [4X[28X[ 1, 2, 3 ][128X[104X
    [4X[25Xgap>[125X [27XD := GeneralisedPetersenGraph(IsMutableDigraph, 5, 2);[127X[104X
    [4X[28X<mutable digraph with 10 vertices, 30 edges>[128X[104X
    [4X[25Xgap>[125X [27XHamiltonianPath(D);[127X[104X
    [4X[28Xfail[128X[104X
  [4X[32X[104X
  
  [1X5.4-34 NrSpanningTrees[101X
  
  [33X[1;0Y[29X[2XNrSpanningTrees[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YAn integer.[133X
  
  [33X[0;0YReturns  the  number  of  spanning  trees  of the symmetric digraph [3Xdigraph[103X.
  [10XNrSpanningTrees[110X will return an error if [3Xdigraph[103X is not a symmetric digraph.[133X
  
  [33X[0;0YSee  [2XIsSymmetricDigraph[102X  ([14X6.2-14[114X)  and  [2XIsUndirectedSpanningTree[102X ([14X4.1-2[114X) for
  more information.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := CompleteDigraph(5);[127X[104X
    [4X[28X<immutable complete digraph with 5 vertices>[128X[104X
    [4X[25Xgap>[125X [27XNrSpanningTrees(D);[127X[104X
    [4X[28X125[128X[104X
    [4X[25Xgap>[125X [27XD := DigraphSymmetricClosure(CycleDigraph(24));;[127X[104X
    [4X[25Xgap>[125X [27XNrSpanningTrees(D);[127X[104X
    [4X[28X24[128X[104X
    [4X[25Xgap>[125X [27XNrSpanningTrees(EmptyDigraph(0));[127X[104X
    [4X[28X0[128X[104X
    [4X[25Xgap>[125X [27XD := GeneralisedPetersenGraph(IsMutableDigraph, 9, 2);[127X[104X
    [4X[28X<mutable digraph with 18 vertices, 54 edges>[128X[104X
    [4X[25Xgap>[125X [27XNrSpanningTrees(D);[127X[104X
    [4X[28X1134225[128X[104X
  [4X[32X[104X
  
  [1X5.4-35 DigraphDijkstra[101X
  
  [33X[1;0Y[29X[2XDigraphDijkstra[102X( [3Xdigraph[103X, [3Xsource[103X, [3Xtarget[103X ) [32X operation[133X
  [33X[1;0Y[29X[2XDigraphDijkstra[102X( [3Xdigraph[103X, [3Xsource[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10YTwo lists.[133X
  
  [33X[0;0YIf  [3Xdigraph[103X is a digraph and [3Xsource[103X and [3Xtarget[103X are vertices of [3Xdigraph[103X, then
  [10XDigraphDijkstra[110X  calculates  the  length of the shortest path from [3Xsource[103X to
  [3Xtarget[103X and returns two lists. Each element of the first list is the distance
  of the corresponding element from [3Xsource[103X. If a vertex was not visited in the
  process  of  calculating  the  shortest distance to [3Xtarget[103X or if there is no
  path  connecting that vertex with [3Xsource[103X, then the corresponding distance is
  [9Xinfinity[109X.  Each  element of the second list gives the previous vertex in the
  shortest  path  from  [3Xsource[103X to the corresponding vertex. For [3Xsource[103X and for
  any vertices that remained unvisited this will be [10X-1[110X.[133X
  
  [33X[0;0YIf  the optional second argument [3Xtarget[103X is not present, then [10XDigraphDijkstra[110X
  returns the shortest path from [3Xsource[103X to every vertex that is reachable from
  [3Xsource[103X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xmat := [[0, 1, 1], [0, 0, 1], [0, 0, 0]];[127X[104X
    [4X[28X[ [ 0, 1, 1 ], [ 0, 0, 1 ], [ 0, 0, 0 ] ][128X[104X
    [4X[25Xgap>[125X [27XD := DigraphByAdjacencyMatrix(mat);[127X[104X
    [4X[28X<immutable digraph with 3 vertices, 3 edges>[128X[104X
    [4X[25Xgap>[125X [27XDigraphDijkstra(D, 2, 3);[127X[104X
    [4X[28X[ [ infinity, 0, 1 ], [ -1, -1, 2 ] ][128X[104X
    [4X[25Xgap>[125X [27XDigraphDijkstra(D, 1, 3);[127X[104X
    [4X[28X[ [ 0, 1, 1 ], [ -1, 1, 1 ] ][128X[104X
    [4X[25Xgap>[125X [27XDigraphDijkstra(D, 1, 2);[127X[104X
    [4X[28X[ [ 0, 1, 1 ], [ -1, 1, 1 ] ][128X[104X
  [4X[32X[104X
  
  
  [1X5.5 [33X[0;0YCayley graphs of groups[133X[101X
  
  [1X5.5-1 GroupOfCayleyDigraph[101X
  
  [33X[1;0Y[29X[2XGroupOfCayleyDigraph[102X( [3Xdigraph[103X ) [32X attribute[133X
  [33X[1;0Y[29X[2XSemigroupOfCayleyDigraph[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA group or semigroup.[133X
  
  [33X[0;0YIf  [3Xdigraph[103X is an immutable Cayley graph of a group [10XG[110X and [3Xdigraph[103X belongs to
  the category [2XIsCayleyDigraph[102X ([14X3.1-4[114X), then [10XGroupOfCayleyDigraph[110X returns [10XG[110X.[133X
  
  [33X[0;0YIf  [3Xdigraph[103X  is  a  Cayley graph of a semigroup [10XS[110X and [3Xdigraph[103X belongs to the
  category [2XIsCayleyDigraph[102X ([14X3.1-4[114X), then [10XSemigroupOfCayleyDigraph[110X returns [10XS[110X.[133X
  
  [33X[0;0YSee also [2XGeneratorsOfCayleyDigraph[102X ([14X5.5-2[114X).[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XG := DihedralGroup(IsPermGroup, 8);[127X[104X
    [4X[28XGroup([ (1,2,3,4), (2,4) ])[128X[104X
    [4X[25Xgap>[125X [27Xdigraph := CayleyDigraph(G);[127X[104X
    [4X[28X<immutable digraph with 8 vertices, 16 edges>[128X[104X
    [4X[25Xgap>[125X [27XGroupOfCayleyDigraph(digraph) = G;[127X[104X
    [4X[28Xtrue[128X[104X
  [4X[32X[104X
  
  [1X5.5-2 GeneratorsOfCayleyDigraph[101X
  
  [33X[1;0Y[29X[2XGeneratorsOfCayleyDigraph[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA list of generators.[133X
  
  [33X[0;0YIf [3Xdigraph[103X is an immutable Cayley graph of a group or semigroup with respect
  to   a   set  of  generators  [10Xgens[110X  and  [3Xdigraph[103X  belongs  to  the  category
  [2XIsCayleyDigraph[102X  ([14X3.1-4[114X),  then [10XGeneratorsOfCayleyDigraph[110X return the list of
  generators [10Xgens[110X over which [3Xdigraph[103X is defined.[133X
  
  [33X[0;0YSee also [2XGroupOfCayleyDigraph[102X ([14X5.5-1[114X) or [2XSemigroupOfCayleyDigraph[102X ([14X5.5-1[114X).[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XG := DihedralGroup(IsPermGroup, 8);[127X[104X
    [4X[28XGroup([ (1,2,3,4), (2,4) ])[128X[104X
    [4X[25Xgap>[125X [27Xdigraph := CayleyDigraph(G);[127X[104X
    [4X[28X<immutable digraph with 8 vertices, 16 edges>[128X[104X
    [4X[25Xgap>[125X [27XGeneratorsOfCayleyDigraph(digraph) = GeneratorsOfGroup(G);[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27Xdigraph := CayleyDigraph(G, [()]);[127X[104X
    [4X[28X<immutable digraph with 8 vertices, 8 edges>[128X[104X
    [4X[25Xgap>[125X [27XGeneratorsOfCayleyDigraph(digraph) = [()];[127X[104X
    [4X[28Xtrue[128X[104X
  [4X[32X[104X
  
  
  [1X5.6 [33X[0;0YAssociated semigroups[133X[101X
  
  [1X5.6-1 AsSemigroup[101X
  
  [33X[1;0Y[29X[2XAsSemigroup[102X( [3Xfilt[103X, [3Xdigraph[103X ) [32X operation[133X
  [33X[1;0Y[29X[2XAsMonoid[102X( [3Xfilt[103X, [3Xdigraph[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10YA semilattice of partial perms.[133X
  
  [33X[0;0YThe    operation    [10XAsSemigroup[110X    requires    that   [3Xfilt[103X   be   equal   to
  [2XIsPartialPermSemigroup[102X  ([14XReference: IsPartialPermSemigroup[114X). If [3Xdigraph[103X is a
  [2XIsJoinSemilatticeDigraph[102X    ([14X6.3-3[114X)   or   [2XIsLatticeDigraph[102X   ([14X6.3-3[114X)   then
  [10XAsSemigroup[110X  returns a semigroup of partial perms which is isomorphic to the
  semigroup  whose  elements  are  the  vertices  of  [3Xdigraph[103X  with the binary
  operation  [2XPartialOrderDigraphJoinOfVertices[102X  ([14X5.3-1[114X).  If [3Xdigraph[103X satisfies
  [2XIsMeetSemilatticeDigraph[102X  ([14X6.3-3[114X)  but  not [2XIsJoinSemilatticeDigraph[102X ([14X6.3-3[114X)
  then [10XAsSemigroup[110X returns a semigroup of partial perms which is isomorphic to
  the  semigroup  whose  elements  are the vertices of [3Xdigraph[103X with the binary
  operation [2XPartialOrderDigraphMeetOfVertices[102X ([14X5.3-1[114X).[133X
  
  [33X[0;0YThe operation [10XAsMonoid[110X behaves similarly to [10XAsSemigroup[110X except that [3Xfilt[103X may
  also  be  equal  to  [2XIsPartialPermMonoid[102X  ([14XReference:  IsPartialPermMonoid[114X),
  [3Xdigraph[103X  must  satisfy  [2XIsLatticeDigraph[102X  ([14X6.3-3[114X),  and the output satisfies
  [2XIsMonoid[102X ([14XReference: IsMonoid[114X).[133X
  
  [33X[0;0YThe output of both of these operations is guaranteed to be of minimal degree
  (see                 [2XDegreeOfPartialPermSemigroup[102X                ([14XReference:
  DegreeOfPartialPermSemigroup[114X)).    Furthermore   the   [2XGeneratorsOfSemigroup[102X
  ([14XReference:  GeneratorsOfSemigroup[114X)  of  the  output is guaranteed to be the
  unique generating set of minimal size.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xdi := Digraph([[1], [1, 2], [1, 3], [1, 4], [1, 2, 3, 5]]);[127X[104X
    [4X[28X<immutable digraph with 5 vertices, 11 edges>[128X[104X
    [4X[25Xgap>[125X [27XS := AsSemigroup(IsPartialPermSemigroup, di);[127X[104X
    [4X[28X<partial perm semigroup of rank 3 with 4 generators>[128X[104X
    [4X[25Xgap>[125X [27XForAll(Elements(S), IsIdempotent);[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27XIsInverseSemigroup(S);[127X[104X
    [4X[28Xtrue[128X[104X
    [4X[25Xgap>[125X [27XSize(S);[127X[104X
    [4X[28X5[128X[104X
    [4X[25Xgap>[125X [27Xdi := Digraph([[1], [1, 2], [1, 2, 3]]);[127X[104X
    [4X[28X<immutable digraph with 3 vertices, 6 edges>[128X[104X
    [4X[25Xgap>[125X [27XM := AsMonoid(IsPartialPermMonoid, di);[127X[104X
    [4X[28X<partial perm monoid of rank 2 with 3 generators>[128X[104X
    [4X[25Xgap>[125X [27XSize(M);[127X[104X
    [4X[28X3[128X[104X
  [4X[32X[104X
  
  [1X5.6-2 AsSemigroup[101X
  
  [33X[1;0Y[29X[2XAsSemigroup[102X( [3Xfilt[103X, [3XY[103X, [3Xgps[103X, [3Xhoms[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10YA Clifford semigroup of partial perms.[133X
  
  [33X[0;0YThe    operation    [10XAsSemigroup[110X    requires    that   [3Xfilt[103X   be   equal   to
  [2XIsPartialPermSemigroup[102X   ([14XReference:  IsPartialPermSemigroup[114X).  If  [3XY[103X  is  a
  [2XIsJoinSemilatticeDigraph[102X ([14X6.3-3[114X) or [2XIsMeetSemilatticeDigraph[102X ([14X6.3-3[114X), [3Xgps[103X is
  a list of groups corresponding to each vertex, and [3Xhoms[103X is a list containing
  for  each edge [10X(i, j)[110X in the transitive reduction of [3Xdigraph[103X a triple [10X[i, j,
  hom][110X  where  [10Xhom[110X  is  a  group  homomorphism  from [10Xgps[i][110X to [10Xgps[j][110X, and the
  diagram  of  homomorphisms commutes, then [10XAsSemigroup[110X returns a semigroup of
  partial  perms  which is isomorphic to the strong semilattice of groups [22XS[Y;
  gps; homs][122X.[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XG1 := AlternatingGroup(4);;[127X[104X
    [4X[25Xgap>[125X [27XG2 := SymmetricGroup(2);;[127X[104X
    [4X[25Xgap>[125X [27XG3 := SymmetricGroup(3);;[127X[104X
    [4X[25Xgap>[125X [27Xgr := Digraph([[1, 3], [2, 3], [3]]);;[127X[104X
    [4X[25Xgap>[125X [27Xsgn := function(x)[127X[104X
    [4X[25X>[125X [27Xif SignPerm(x) = 1 then[127X[104X
    [4X[25X>[125X [27Xreturn ();[127X[104X
    [4X[25X>[125X [27Xfi;[127X[104X
    [4X[25X>[125X [27Xreturn (1, 2);[127X[104X
    [4X[25X>[125X [27Xend;;[127X[104X
    [4X[25Xgap>[125X [27Xhom13 := GroupHomomorphismByFunction(G1, G3, sgn);;[127X[104X
    [4X[25Xgap>[125X [27Xhom23 := GroupHomomorphismByFunction(G2, G3, sgn);;[127X[104X
    [4X[25Xgap>[125X [27XT := AsSemigroup(IsPartialPermSemigroup,[127X[104X
    [4X[25X>[125X [27Xgr,[127X[104X
    [4X[25X>[125X [27X[G1, G2, G3], [[1, 3, hom13], [2, 3, hom23]]);;[127X[104X
    [4X[25Xgap>[125X [27XSize(T);[127X[104X
    [4X[28X20[128X[104X
    [4X[25Xgap>[125X [27XD := GreensDClasses(T);;[127X[104X
    [4X[25Xgap>[125X [27XList(D, x -> Size(x));[127X[104X
    [4X[28X[ 6, 12, 2 ][128X[104X
  [4X[32X[104X
  
  
  [1X5.7 [33X[0;0YPlanarity[133X[101X
  
  [1X5.7-1 KuratowskiPlanarSubdigraph[101X
  
  [33X[1;0Y[29X[2XKuratowskiPlanarSubdigraph[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA list or [9Xfail[109X.[133X
  
  [33X[0;0Y[10XKuratowskiPlanarSubdigraph[110X   returns   the   immutable   list  of  lists  of
  out-neighbours  of  a  (not  necessarily  induced) subdigraph of the digraph
  [3Xdigraph[103X  that  witnesses  the  fact  that  [3Xdigraph[103X is not planar, or [9Xfail[109X if
  [3Xdigraph[103X  is  planar.  In other words, [10XKuratowskiPlanarSubdigraph[110X returns the
  out-neighbours  of  a  subdigraph  of  [3Xdigraph[103X  that  is homeomorphic to the
  complete  graph  with  [10X5[110X  vertices,  or to the complete bipartite graph with
  vertex sets of sizes [10X3[110X and [10X3[110X.[133X
  
  [33X[0;0YThe  directions  and multiplicities of any edges in [3Xdigraph[103X are ignored when
  considering whether or not [3Xdigraph[103X is planar.[133X
  
  [33X[0;0YSee also [2XIsPlanarDigraph[102X ([14X6.6-1[114X) and [2XSubdigraphHomeomorphicToK33[102X ([14X5.7-5[114X).[133X
  
  [33X[0;0YThis      method      uses      the      reference     implementation     in
  [5Xedge-addition-planarity-suite[105X  by  John Boyer of the algorithms described in
  [BM06].[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[3, 5, 10], [8, 9, 10], [1, 4], [3, 6], [127X[104X
    [4X[25X>[125X [27X[1, 7, 11], [4, 7], [6, 8], [2, 7], [2, 11], [1, 2], [5, 9]]);[127X[104X
    [4X[28X<immutable digraph with 11 vertices, 25 edges>[128X[104X
    [4X[25Xgap>[125X [27XKuratowskiPlanarSubdigraph(D);[127X[104X
    [4X[28Xfail[128X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[2, 4, 7, 9, 10], [1, 3, 4, 6, 9, 10], [6, 10], [127X[104X
    [4X[25X>[125X [27X[2, 5, 8, 9], [1, 2, 3, 4, 6, 7, 9, 10], [3, 4, 5, 7, 9, 10], [127X[104X
    [4X[25X>[125X [27X[3, 4, 5, 6, 9, 10], [3, 4, 5, 7, 9], [2, 3, 5, 6, 7, 8], [3, 5]]);[127X[104X
    [4X[28X<immutable digraph with 10 vertices, 50 edges>[128X[104X
    [4X[25Xgap>[125X [27XIsPlanarDigraph(D);[127X[104X
    [4X[28Xfalse[128X[104X
    [4X[25Xgap>[125X [27XKuratowskiPlanarSubdigraph(D);[127X[104X
    [4X[28X[ [ 2, 9, 7 ], [ 3 ], [ 6 ], [ 5, 9 ], [ 6 ], [  ], [ 4 ], [128X[104X
    [4X[28X  [ 7, 9, 3 ], [  ], [  ] ][128X[104X
    [4X[25Xgap>[125X [27XD := Digraph(IsMutableDigraph, [[3, 5, 10], [8, 9, 10], [1, 4],[127X[104X
    [4X[25X>[125X [27X[3, 6], [1, 7, 11], [4, 7], [6, 8], [2, 7], [2, 11], [1, 2], [5, 9]]);[127X[104X
    [4X[28X<mutable digraph with 11 vertices, 25 edges>[128X[104X
    [4X[25Xgap>[125X [27XKuratowskiPlanarSubdigraph(D);[127X[104X
    [4X[28Xfail[128X[104X
    [4X[25Xgap>[125X [27XD := Digraph(IsMutableDigraph, [[2, 4, 7, 9, 10],[127X[104X
    [4X[25X>[125X [27X[1, 3, 4, 6, 9, 10], [6, 10], [2, 5, 8, 9],[127X[104X
    [4X[25X>[125X [27X[1, 2, 3, 4, 6, 7, 9, 10], [3, 4, 5, 7, 9, 10],[127X[104X
    [4X[25X>[125X [27X[3, 4, 5, 6, 9, 10], [3, 4, 5, 7, 9], [2, 3, 5, 6, 7, 8], [3, 5]]);[127X[104X
    [4X[28X<mutable digraph with 10 vertices, 50 edges>[128X[104X
    [4X[25Xgap>[125X [27XIsPlanarDigraph(D);[127X[104X
    [4X[28Xfalse[128X[104X
    [4X[25Xgap>[125X [27XKuratowskiPlanarSubdigraph(D);[127X[104X
    [4X[28X[ [ 2, 9, 7 ], [ 3 ], [ 6 ], [ 5, 9 ], [ 6 ], [  ], [ 4 ], [128X[104X
    [4X[28X  [ 7, 9, 3 ], [  ], [  ] ][128X[104X
  [4X[32X[104X
  
  [1X5.7-2 KuratowskiOuterPlanarSubdigraph[101X
  
  [33X[1;0Y[29X[2XKuratowskiOuterPlanarSubdigraph[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA list or [9Xfail[109X.[133X
  
  [33X[0;0Y[10XKuratowskiOuterPlanarSubdigraph[110X  returns  the  immutable  list  of immutable
  lists  of  out-neighbours  of  a (not necessarily induced) subdigraph of the
  digraph [3Xdigraph[103X that witnesses the fact that [3Xdigraph[103X is not outer planar, or
  [9Xfail[109X     if     [3Xdigraph[103X     is     outer    planar.    In    other    words,
  [10XKuratowskiOuterPlanarSubdigraph[110X  returns  the out-neighbours of a subdigraph
  of [3Xdigraph[103X that is homeomorphic to the complete graph with [10X4[110X vertices, or to
  the complete bipartite graph with vertex sets of sizes [10X2[110X and [10X3[110X.[133X
  
  [33X[0;0YThe  directions  and multiplicities of any edges in [3Xdigraph[103X are ignored when
  considering whether or not [3Xdigraph[103X is outer planar.[133X
  
  [33X[0;0YSee  also  [2XIsOuterPlanarDigraph[102X ([14X6.6-2[114X), [2XSubdigraphHomeomorphicToK4[102X ([14X5.7-5[114X),
  and [2XSubdigraphHomeomorphicToK23[102X ([14X5.7-5[114X).[133X
  
  [33X[0;0YThis      method      uses      the      reference     implementation     in
  [5Xedge-addition-planarity-suite[105X  by  John Boyer of the algorithms described in
  [BM06].[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[3, 5, 10], [8, 9, 10], [1, 4], [3, 6], [127X[104X
    [4X[25X>[125X [27X[1, 7, 11], [4, 7], [6, 8], [2, 7], [2, 11], [1, 2], [5, 9]]);[127X[104X
    [4X[28X<immutable digraph with 11 vertices, 25 edges>[128X[104X
    [4X[25Xgap>[125X [27XKuratowskiOuterPlanarSubdigraph(D);[127X[104X
    [4X[28X[ [ 3, 5, 10 ], [ 9, 8, 10 ], [ 4 ], [ 6 ], [ 11 ], [ 7 ], [ 8 ], [128X[104X
    [4X[28X  [  ], [ 11 ], [  ], [  ] ][128X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[2, 4, 7, 9, 10], [1, 3, 4, 6, 9, 10], [6, 10], [127X[104X
    [4X[25X>[125X [27X[2, 5, 8, 9], [1, 2, 3, 4, 6, 7, 9, 10], [3, 4, 5, 7, 9, 10], [127X[104X
    [4X[25X>[125X [27X[3, 4, 5, 6, 9, 10], [3, 4, 5, 7, 9], [2, 3, 5, 6, 7, 8], [3, 5]]);[127X[104X
    [4X[28X<immutable digraph with 10 vertices, 50 edges>[128X[104X
    [4X[25Xgap>[125X [27XIsOuterPlanarDigraph(D);[127X[104X
    [4X[28Xfalse[128X[104X
    [4X[25Xgap>[125X [27XKuratowskiOuterPlanarSubdigraph(D);[127X[104X
    [4X[28X[ [  ], [  ], [  ], [ 8, 9 ], [  ], [  ], [ 9, 4 ], [ 7, 9 ], [  ], [128X[104X
    [4X[28X  [  ] ][128X[104X
    [4X[25Xgap>[125X [27XD := Digraph(IsMutableDigraph, [[3, 5, 10], [8, 9, 10], [1, 4],[127X[104X
    [4X[25X>[125X [27X[3, 6], [1, 7, 11], [4, 7], [6, 8], [2, 7], [2, 11], [1, 2], [5, 9]]);[127X[104X
    [4X[28X<mutable digraph with 11 vertices, 25 edges>[128X[104X
    [4X[25Xgap>[125X [27XKuratowskiOuterPlanarSubdigraph(D);[127X[104X
    [4X[28X[ [ 3, 5, 10 ], [ 9, 8, 10 ], [ 4 ], [ 6 ], [ 11 ], [ 7 ], [ 8 ], [128X[104X
    [4X[28X  [  ], [ 11 ], [  ], [  ] ][128X[104X
    [4X[25Xgap>[125X [27XD := Digraph(IsMutableDigraph, [[2, 4, 7, 9, 10],[127X[104X
    [4X[25X>[125X [27X[1, 3, 4, 6, 9, 10], [6, 10], [2, 5, 8, 9],[127X[104X
    [4X[25X>[125X [27X[1, 2, 3, 4, 6, 7, 9, 10], [3, 4, 5, 7, 9, 10],[127X[104X
    [4X[25X>[125X [27X[3, 4, 5, 6, 9, 10], [3, 4, 5, 7, 9], [2, 3, 5, 6, 7, 8], [3, 5]]);[127X[104X
    [4X[28X<mutable digraph with 10 vertices, 50 edges>[128X[104X
    [4X[25Xgap>[125X [27XIsOuterPlanarDigraph(D);[127X[104X
    [4X[28Xfalse[128X[104X
    [4X[25Xgap>[125X [27XKuratowskiOuterPlanarSubdigraph(D);[127X[104X
    [4X[28X[ [  ], [  ], [  ], [ 8, 9 ], [  ], [  ], [ 9, 4 ], [ 7, 9 ], [  ], [128X[104X
    [4X[28X  [  ] ][128X[104X
  [4X[32X[104X
  
  [1X5.7-3 PlanarEmbedding[101X
  
  [33X[1;0Y[29X[2XPlanarEmbedding[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA list or [9Xfail[109X.[133X
  
  [33X[0;0YIf  [3Xdigraph[103X  is a planar digraph, then [10XPlanarEmbedding[110X returns the immutable
  list  of  lists  of out-neighbours of a subdigraph of [3Xdigraph[103X such that each
  vertex's  neighbours are given in clockwise order. If [3Xdigraph[103X is not planar,
  then [9Xfail[109X is returned.[133X
  
  [33X[0;0YThe  directions  and  multiplicities  of any edges in [3Xdigraph[103X are ignored by
  [10XPlanarEmbedding[110X.[133X
  
  [33X[0;0YSee also [2XIsPlanarDigraph[102X ([14X6.6-1[114X).[133X
  
  [33X[0;0YThis      method      uses      the      reference     implementation     in
  [5Xedge-addition-planarity-suite[105X  by  John Boyer of the algorithms described in
  [BM06].[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[3, 5, 10], [8, 9, 10], [1, 4], [3, 6], [127X[104X
    [4X[25X>[125X [27X[1, 7, 11], [4, 7], [6, 8], [2, 7], [2, 11], [1, 2], [5, 9]]);[127X[104X
    [4X[28X<immutable digraph with 11 vertices, 25 edges>[128X[104X
    [4X[25Xgap>[125X [27XPlanarEmbedding(D);[127X[104X
    [4X[28X[ [ 3, 10, 5 ], [ 10, 8, 9 ], [ 4 ], [ 6 ], [ 11, 7 ], [ 7 ], [ 8 ], [128X[104X
    [4X[28X  [  ], [ 11 ], [  ], [  ] ][128X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[2, 4, 7, 9, 10], [1, 3, 4, 6, 9, 10], [6, 10], [127X[104X
    [4X[25X>[125X [27X[2, 5, 8, 9], [1, 2, 3, 4, 6, 7, 9, 10], [3, 4, 5, 7, 9, 10], [127X[104X
    [4X[25X>[125X [27X[3, 4, 5, 6, 9, 10], [3, 4, 5, 7, 9], [2, 3, 5, 6, 7, 8], [3, 5]]);[127X[104X
    [4X[28X<immutable digraph with 10 vertices, 50 edges>[128X[104X
    [4X[25Xgap>[125X [27XPlanarEmbedding(D);[127X[104X
    [4X[28Xfail[128X[104X
    [4X[25Xgap>[125X [27XD := Digraph(IsMutableDigraph, [[3, 5, 10], [8, 9, 10], [1, 4],[127X[104X
    [4X[25X>[125X [27X[3, 6], [1, 7, 11], [4, 7], [6, 8], [2, 7], [2, 11], [1, 2], [5, 9]]);[127X[104X
    [4X[28X<mutable digraph with 11 vertices, 25 edges>[128X[104X
    [4X[25Xgap>[125X [27XPlanarEmbedding(D);[127X[104X
    [4X[28X[ [ 3, 10, 5 ], [ 10, 8, 9 ], [ 4 ], [ 6 ], [ 11, 7 ], [ 7 ], [ 8 ], [128X[104X
    [4X[28X  [  ], [ 11 ], [  ], [  ] ][128X[104X
    [4X[25Xgap>[125X [27XD := Digraph(IsMutableDigraph, [[2, 4, 7, 9, 10],[127X[104X
    [4X[25X>[125X [27X[1, 3, 4, 6, 9, 10], [6, 10], [2, 5, 8, 9],[127X[104X
    [4X[25X>[125X [27X[1, 2, 3, 4, 6, 7, 9, 10], [3, 4, 5, 7, 9, 10],[127X[104X
    [4X[25X>[125X [27X[3, 4, 5, 6, 9, 10], [3, 4, 5, 7, 9], [2, 3, 5, 6, 7, 8], [3, 5]]);[127X[104X
    [4X[28X<mutable digraph with 10 vertices, 50 edges>[128X[104X
    [4X[25Xgap>[125X [27XPlanarEmbedding(D);[127X[104X
    [4X[28Xfail[128X[104X
  [4X[32X[104X
  
  [1X5.7-4 OuterPlanarEmbedding[101X
  
  [33X[1;0Y[29X[2XOuterPlanarEmbedding[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA list or [9Xfail[109X.[133X
  
  [33X[0;0YIf [3Xdigraph[103X is an outer planar digraph, then [10XOuterPlanarEmbedding[110X returns the
  immutable  list  of  lists of out-neighbours of a subdigraph of [3Xdigraph[103X such
  that  each  vertex's  neighbours are given in clockwise order. If [3Xdigraph[103X is
  not outer planar, then [9Xfail[109X is returned.[133X
  
  [33X[0;0YThe  directions  and  multiplicities  of any edges in [3Xdigraph[103X are ignored by
  [10XOuterPlanarEmbedding[110X.[133X
  
  [33X[0;0YSee also [2XIsOuterPlanarDigraph[102X ([14X6.6-2[114X).[133X
  
  [33X[0;0YThis      method      uses      the      reference     implementation     in
  [5Xedge-addition-planarity-suite[105X  by  John Boyer of the algorithms described in
  [BM06].[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[3, 5, 10], [8, 9, 10], [1, 4], [3, 6], [127X[104X
    [4X[25X>[125X [27X[1, 7, 11], [4, 7], [6, 8], [2, 7], [2, 11], [1, 2], [5, 9]]);[127X[104X
    [4X[28X<immutable digraph with 11 vertices, 25 edges>[128X[104X
    [4X[25Xgap>[125X [27XOuterPlanarEmbedding(D);[127X[104X
    [4X[28Xfail[128X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[2, 4, 7, 9, 10], [1, 3, 4, 6, 9, 10], [6, 10], [127X[104X
    [4X[25X>[125X [27X[2, 5, 8, 9], [1, 2, 3, 4, 6, 7, 9, 10], [3, 4, 5, 7, 9, 10], [127X[104X
    [4X[25X>[125X [27X[3, 4, 5, 6, 9, 10], [3, 4, 5, 7, 9], [2, 3, 5, 6, 7, 8], [3, 5]]);[127X[104X
    [4X[28X<immutable digraph with 10 vertices, 50 edges>[128X[104X
    [4X[25Xgap>[125X [27XOuterPlanarEmbedding(D);[127X[104X
    [4X[28Xfail[128X[104X
    [4X[25Xgap>[125X [27XOuterPlanarEmbedding(CompleteBipartiteDigraph(2, 2));[127X[104X
    [4X[28X[ [ 3, 4 ], [ 4, 3 ], [  ], [  ] ][128X[104X
    [4X[25Xgap>[125X [27XD := Digraph(IsMutableDigraph, [[3, 5, 10], [8, 9, 10], [1, 4],[127X[104X
    [4X[25X>[125X [27X[3, 6], [1, 7, 11], [4, 7], [6, 8], [2, 7], [2, 11], [1, 2], [5, 9]]);[127X[104X
    [4X[28X<mutable digraph with 11 vertices, 25 edges>[128X[104X
    [4X[25Xgap>[125X [27XOuterPlanarEmbedding(D);[127X[104X
    [4X[28Xfail[128X[104X
    [4X[25Xgap>[125X [27XD := Digraph(IsMutableDigraph, [[2, 4, 7, 9, 10],[127X[104X
    [4X[25X>[125X [27X[1, 3, 4, 6, 9, 10], [6, 10], [2, 5, 8, 9],[127X[104X
    [4X[25X>[125X [27X[1, 2, 3, 4, 6, 7, 9, 10], [3, 4, 5, 7, 9, 10],[127X[104X
    [4X[25X>[125X [27X[3, 4, 5, 6, 9, 10], [3, 4, 5, 7, 9], [2, 3, 5, 6, 7, 8], [3, 5]]);[127X[104X
    [4X[28X<mutable digraph with 10 vertices, 50 edges>[128X[104X
    [4X[25Xgap>[125X [27XOuterPlanarEmbedding(D);[127X[104X
    [4X[28Xfail[128X[104X
    [4X[25Xgap>[125X [27XOuterPlanarEmbedding(CompleteBipartiteDigraph(2, 2));[127X[104X
    [4X[28X[ [ 3, 4 ], [ 4, 3 ], [  ], [  ] ][128X[104X
  [4X[32X[104X
  
  [1X5.7-5 SubdigraphHomeomorphicToK23[101X
  
  [33X[1;0Y[29X[2XSubdigraphHomeomorphicToK23[102X( [3Xdigraph[103X ) [32X attribute[133X
  [33X[1;0Y[29X[2XSubdigraphHomeomorphicToK33[102X( [3Xdigraph[103X ) [32X attribute[133X
  [33X[1;0Y[29X[2XSubdigraphHomeomorphicToK4[102X( [3Xdigraph[103X ) [32X attribute[133X
  [6XReturns:[106X  [33X[0;10YA list or [9Xfail[109X.[133X
  
  [33X[0;0YThese  attributes  return the immutable list of lists of out-neighbours of a
  subdigraph  of  the  digraph  [3Xdigraph[103X  which  is  homeomorphic to one of the
  following:  the  complete bipartite graph with vertex sets of sizes [10X2[110X and [10X3[110X;
  the  complete  bipartite  graph  with  vertex  sets of sizes [10X3[110X and [10X3[110X; or the
  complete  graph  with  [10X4[110X  vertices. If [3Xdigraph[103X has no such subdigraphs, then
  [9Xfail[109X is returned.[133X
  
  [33X[0;0YSee  also  [2XIsPlanarDigraph[102X ([14X6.6-1[114X) and [2XIsOuterPlanarDigraph[102X ([14X6.6-2[114X) for more
  details.[133X
  
  [33X[0;0YThis      method      uses      the      reference     implementation     in
  [5Xedge-addition-planarity-suite[105X  by  John Boyer of the algorithms described in
  [BM06].[133X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[3, 5, 10], [8, 9, 10], [1, 4], [3, 6], [1, 7, 11], [127X[104X
    [4X[25X>[125X [27X[4, 7], [6, 8], [2, 7], [2, 11], [1, 2], [5, 9]]);[127X[104X
    [4X[28X<immutable digraph with 11 vertices, 25 edges>[128X[104X
    [4X[25Xgap>[125X [27XSubdigraphHomeomorphicToK4(D);[127X[104X
    [4X[28X[ [ 3, 5, 10 ], [ 9, 8, 10 ], [ 4 ], [ 6 ], [ 7, 11 ], [ 7 ], [ 8 ], [128X[104X
    [4X[28X  [  ], [ 11 ], [  ], [  ] ][128X[104X
    [4X[25Xgap>[125X [27XSubdigraphHomeomorphicToK23(D);[127X[104X
    [4X[28X[ [ 3, 5, 10 ], [ 9, 8, 10 ], [ 4 ], [ 6 ], [ 11 ], [ 7 ], [ 8 ], [128X[104X
    [4X[28X  [  ], [ 11 ], [  ], [  ] ][128X[104X
    [4X[25Xgap>[125X [27XD := Digraph([[3, 5, 10], [8, 9, 10], [1, 4], [3, 6], [1, 11], [127X[104X
    [4X[25X>[125X [27X [4, 7], [6, 8], [2, 7], [2, 11], [1, 2], [5, 9]]);[127X[104X
    [4X[28X<immutable digraph with 11 vertices, 24 edges>[128X[104X
    [4X[25Xgap>[125X [27XSubdigraphHomeomorphicToK4(D);[127X[104X
    [4X[28Xfail[128X[104X
    [4X[25Xgap>[125X [27XSubdigraphHomeomorphicToK23(D);[127X[104X
    [4X[28X[ [ 3, 10, 5 ], [ 10, 8, 9 ], [ 4 ], [ 6 ], [ 11 ], [ 7 ], [ 8 ], [128X[104X
    [4X[28X  [  ], [ 11 ], [  ], [  ] ][128X[104X
    [4X[25Xgap>[125X [27XSubdigraphHomeomorphicToK33(D);[127X[104X
    [4X[28Xfail[128X[104X
    [4X[25Xgap>[125X [27XSubdigraphHomeomorphicToK23(NullDigraph(0));[127X[104X
    [4X[28Xfail[128X[104X
    [4X[25Xgap>[125X [27XSubdigraphHomeomorphicToK33(CompleteDigraph(5));[127X[104X
    [4X[28Xfail[128X[104X
    [4X[25Xgap>[125X [27XSubdigraphHomeomorphicToK33(CompleteBipartiteDigraph(3, 3));[127X[104X
    [4X[28X[ [ 4, 6, 5 ], [ 4, 5, 6 ], [ 6, 5, 4 ], [  ], [  ], [  ] ][128X[104X
    [4X[25Xgap>[125X [27XSubdigraphHomeomorphicToK4(CompleteDigraph(3));[127X[104X
    [4X[28Xfail[128X[104X
    [4X[25Xgap>[125X [27XD := Digraph(IsMutableDigraph, [[3, 5, 10], [8, 9, 10], [1, 4],[127X[104X
    [4X[25X>[125X [27X[3, 6], [1, 7, 11], [4, 7], [6, 8], [2, 7], [2, 11], [1, 2], [5, 9]]);[127X[104X
    [4X[28X<mutable digraph with 11 vertices, 25 edges>[128X[104X
    [4X[25Xgap>[125X [27XSubdigraphHomeomorphicToK4(D);[127X[104X
    [4X[28X[ [ 3, 5, 10 ], [ 9, 8, 10 ], [ 4 ], [ 6 ], [ 7, 11 ], [ 7 ], [ 8 ], [128X[104X
    [4X[28X  [  ], [ 11 ], [  ], [  ] ][128X[104X
    [4X[25Xgap>[125X [27XSubdigraphHomeomorphicToK23(D);[127X[104X
    [4X[28X[ [ 3, 5, 10 ], [ 9, 8, 10 ], [ 4 ], [ 6 ], [ 11 ], [ 7 ], [ 8 ], [128X[104X
    [4X[28X  [  ], [ 11 ], [  ], [  ] ][128X[104X
    [4X[25Xgap>[125X [27XD := Digraph(IsMutableDigraph, [[3, 5, 10], [8, 9, 10], [1, 4],[127X[104X
    [4X[25X>[125X [27X[3, 6], [1, 11], [4, 7], [6, 8], [2, 7], [2, 11], [1, 2], [5, 9]]);[127X[104X
    [4X[28X<mutable digraph with 11 vertices, 24 edges>[128X[104X
    [4X[25Xgap>[125X [27XSubdigraphHomeomorphicToK4(D);[127X[104X
    [4X[28Xfail[128X[104X
    [4X[25Xgap>[125X [27XSubdigraphHomeomorphicToK23(D);[127X[104X
    [4X[28X[ [ 3, 10, 5 ], [ 10, 8, 9 ], [ 4 ], [ 6 ], [ 11 ], [ 7 ], [ 8 ], [128X[104X
    [4X[28X  [  ], [ 11 ], [  ], [  ] ][128X[104X
    [4X[25Xgap>[125X [27XSubdigraphHomeomorphicToK33(D);[127X[104X
    [4X[28Xfail[128X[104X
    [4X[25Xgap>[125X [27XSubdigraphHomeomorphicToK23(NullDigraph(0));[127X[104X
    [4X[28Xfail[128X[104X
    [4X[25Xgap>[125X [27XSubdigraphHomeomorphicToK33(CompleteDigraph(5));[127X[104X
    [4X[28Xfail[128X[104X
    [4X[25Xgap>[125X [27XSubdigraphHomeomorphicToK33(CompleteBipartiteDigraph(3, 3));[127X[104X
    [4X[28X[ [ 4, 6, 5 ], [ 4, 5, 6 ], [ 6, 5, 4 ], [  ], [  ], [  ] ][128X[104X
    [4X[25Xgap>[125X [27XSubdigraphHomeomorphicToK4(CompleteDigraph(3));[127X[104X
    [4X[28Xfail[128X[104X
  [4X[32X[104X
  
