  
  [1X10 [33X[0;0YOrdered Set Datastructures[133X[101X
  
  [33X[0;0YIn  this  chapter  we deal with datastructures designed to represent sets of
  objects which have an intrinsic ordering. Such datastructures should support
  fast  (possibly  amortised) [23XO(\log n)[123X addition, deletion and membership test
  operations  and  allow  efficient  iteration  through all the objects in the
  datastructure  in  the  order  determined  by the given comparison function.
  Since  they  represent  a set, adding an object equal to one already present
  has no effect.[133X
  
  [33X[0;0YWe  refer  to these as ordered set [13Xdatastructure[113X because the differ from the
  [5XGAP[105X notion of a set in a number of ways:[133X
  
  [30X    [33X[0;6YThey  all  lie  in  a  common  family  [10XOrderedSetDSFamily[110X  and  pay no
        attention to the families of the objects stored in them.[133X
  
  [30X    [33X[0;6YEquality  of  these  structures  is  by  identity, not equality of the
        represented set[133X
  
  [30X    [33X[0;6YThe ordering of the objects in the set does not have to be default [5XGAP[105X
        ordering  "less than", but is determined by the attribute [2XLessFunction[102X
        ([14X10.2-13[114X)[133X
  
  [33X[0;0YThree implementations of ordered set data structures are currently included:
  skiplists,  binary  search  trees  and (as a specialisation of binary search
  trees)  AVL  trees.  AVL trees seem to be the fastest in general, and memory
  usage is similar. More details to come[133X
  
  
  [1X10.1 [33X[0;0YUsage[133X[101X
  
  [4X[32X  Example  [32X[104X
    [4X[25Xgap>[125X [27Xs := OrderedSetDS(IsSkipListRep, {x,y} -> String(x) < String(y));[127X[104X
    [4X[28X<skiplist 0 entries>[128X[104X
    [4X[25Xgap>[125X [27XAddset(s, 1);[127X[104X
    [4X[25Xgap>[125X [27XAddSet(s, 2);[127X[104X
    [4X[25Xgap>[125X [27XAddSet(s, 10);[127X[104X
    [4X[25Xgap>[125X [27XAddSet(s, (1,2,3));[127X[104X
    [4X[25Xgap>[125X [27XRemoveSet(s, (1,2,3));[127X[104X
    [4X[28X1[128X[104X
    [4X[25Xgap>[125X [27XAsListSorted(s);[127X[104X
    [4X[28X[ 1, 10, 2 ][128X[104X
    [4X[28X[128X[104X
    [4X[25Xgap>[125X [27Xb := OrderedSetDS(IsBinarySearchTreeRep, Primes);[127X[104X
    [4X[28X<bst size 168>[128X[104X
    [4X[25Xgap>[125X [27X91 in b;[127X[104X
    [4X[28Xfalse[128X[104X
    [4X[25Xgap>[125X [27X97 in b;[127X[104X
    [4X[28Xtrue[128X[104X
  [4X[32X[104X
  
  
  [1X10.2 [33X[0;0YAPI[133X[101X
  
  [33X[0;0YEvery implementation of an ordered set datastructure must follow the API set
  out below[133X
  
  [1X10.2-1 IsOrderedSetDS[101X
  
  [33X[1;0Y[29X[2XIsOrderedSetDS[102X( [3Xarg[103X ) [32X filter[133X
  [6XReturns:[106X  [33X[0;10Y[9Xtrue[109X or [9Xfalse[109X[133X
  
  [33X[0;0YCategory of ordered set.[133X
  
  [1X10.2-2 IsStandardOrderedSetDS[101X
  
  [33X[1;0Y[29X[2XIsStandardOrderedSetDS[102X( [3Xarg[103X ) [32X filter[133X
  [6XReturns:[106X  [33X[0;10Y[9Xtrue[109X or [9Xfalse[109X[133X
  
  [33X[0;0YSubcategory of ordered sets where the ordering is [5XGAP[105X's default [10X<[110X[133X
  
  [1X10.2-3 OrderedSetDS[101X
  
  [33X[1;0Y[29X[2XOrderedSetDS[102X( [3Xfilter[103X[, [3XlessThan[103X[, [3XinitialEntries[103X[, [3XrandomSource[103X]]] ) [32X constructor[133X
  [6XReturns:[106X  [33X[0;10Yan ordered set datastructure[133X
  
  [33X[0;0YThe  family  that  contains all ordered set datastructures. Constructors for
  ordered sets[133X
  
  [33X[0;0YThe  argument  [3Xfilter[103X is a filter that the resulting ordered set object will
  have.[133X
  
  [33X[0;0YThe  optional  argument [3XlessThan[103X must be a binary function that returns [9Xtrue[109X
  if its first argument is less than its second argument, and [9Xfalse[109X otherwise.
  The default [3XlessThan[103X is [5XGAP[105X's built in [10X<[110X.[133X
  
  [33X[0;0YThe  optional  argument  [3X initialEntries[103X gives a collection of elements that
  the ordered set is initialised with, and defaults to the empty set.[133X
  
  [33X[0;0YThe  optional  argument  [3XrandomSource[103X  is  useful  in  a  number of possible
  implementations  that  use  randomised  methods  to  achieve  good amortised
  complexity  with high probability and simple data structures. It defaults to
  the global Mersenne twister.[133X
  
  [1X10.2-4 OrderedSetDS[101X
  
  [33X[1;0Y[29X[2XOrderedSetDS[102X( [3Xarg1[103X, [3Xarg2[103X, [3Xarg3[103X ) [32X constructor[133X
  
  [1X10.2-5 OrderedSetDS[101X
  
  [33X[1;0Y[29X[2XOrderedSetDS[102X( [3Xarg1[103X, [3Xarg2[103X, [3Xarg3[103X ) [32X constructor[133X
  
  [1X10.2-6 OrderedSetDS[101X
  
  [33X[1;0Y[29X[2XOrderedSetDS[102X( [3Xarg1[103X, [3Xarg2[103X, [3Xarg3[103X ) [32X constructor[133X
  
  [1X10.2-7 OrderedSetDS[101X
  
  [33X[1;0Y[29X[2XOrderedSetDS[102X( [3Xarg1[103X, [3Xarg2[103X ) [32X constructor[133X
  
  [1X10.2-8 OrderedSetDS[101X
  
  [33X[1;0Y[29X[2XOrderedSetDS[102X( [3Xarg1[103X, [3Xarg2[103X ) [32X constructor[133X
  
  [1X10.2-9 OrderedSetDS[101X
  
  [33X[1;0Y[29X[2XOrderedSetDS[102X( [3Xarg[103X ) [32X constructor[133X
  
  [1X10.2-10 AddSet[101X
  
  [33X[1;0Y[29X[2XAddSet[102X( [3Xset[103X, [3Xobject[103X ) [32X operation[133X
  
  [33X[0;0YOther  constructors  cover  making  an ordered set from another ordered set,
  from  an  iterator,  from a function and an iterator, or from a function, an
  iterator and a random source.[133X
  
  [33X[0;0YAdds [3Xobject[103X to [3Xset[103X. Does nothing if [3Xobject[103X[10Xin[110X[3Xset[103Xset.[133X
  
  [1X10.2-11 RemoveSet[101X
  
  [33X[1;0Y[29X[2XRemoveSet[102X( [3Xset[103X, [3Xobject[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10Y[9X0[109X or [9X1[109X[133X
  
  [33X[0;0YRemoves  [3Xobject[103X  from  [3Xset[103X  if  present, and returns the number of copies of
  [3Xobject[103X  that  were  in  [3Xset[103X,  that  is  [9X0[109X  or  [9X1[109X.  This for consistency with
  multisets.[133X
  
  [1X10.2-12 \in[101X
  
  [33X[1;0Y[29X[2X\in[102X( [3Xobject[103X, [3Xset[103X ) [32X operation[133X
  
  [33X[0;0YAll  objects  in  IsOrderedSetDS  must  implement \in, which returns [3Xtrue[103X if
  [3Xobject[103X is present in [3Xset[103X and [9Xfalse[109X otherwise.[133X
  
  [1X10.2-13 LessFunction[101X
  
  [33X[1;0Y[29X[2XLessFunction[102X( [3Xset[103X ) [32X attribute[133X
  
  [33X[0;0YThe binary function to perform the comparison for elements of the set.[133X
  
  [1X10.2-14 Size[101X
  
  [33X[1;0Y[29X[2XSize[102X( [3Xset[103X ) [32X attribute[133X
  
  [33X[0;0YThe number of objects in the set[133X
  
  [1X10.2-15 IteratorSorted[101X
  
  [33X[1;0Y[29X[2XIteratorSorted[102X( [3Xset[103X ) [32X operation[133X
  [6XReturns:[106X  [33X[0;10Yiterator[133X
  
  [33X[0;0YReturns  an iterator of [3Xset[103X that can be used to iterate through the elements
  of [3Xset[103X in the order imposed by [2XLessFunction[102X ([14X10.2-13[114X).[133X
  
  
  [1X10.3 [33X[0;0YDefault methods[133X[101X
  
  [33X[0;0YDefault  methods  based  on  [2XIteratorSorted[102X  ([14XReference: IteratorSorted[114X) are
  installed for the following operations and attributes, but can be overridden
  for data structures that support better algorithms.[133X
  
  [1X10.3-1 Iterator[101X
  
  [33X[1;0Y[29X[2XIterator[102X( [3Xarg[103X ) [32X operation[133X
  
  [1X10.3-2 AsSSortedList[101X
  
  [33X[1;0Y[29X[2XAsSSortedList[102X( [3Xarg[103X ) [32X attribute[133X
  
  [1X10.3-3 AsSortedList[101X
  
  [33X[1;0Y[29X[2XAsSortedList[102X( [3Xarg[103X ) [32X attribute[133X
  
  [1X10.3-4 AsList[101X
  
  [33X[1;0Y[29X[2XAsList[102X( [3Xarg[103X ) [32X attribute[133X
  
  [1X10.3-5 EnumeratorSorted[101X
  
  [33X[1;0Y[29X[2XEnumeratorSorted[102X( [3Xarg[103X ) [32X attribute[133X
  
  [1X10.3-6 Enumerator[101X
  
  [33X[1;0Y[29X[2XEnumerator[102X( [3Xarg[103X ) [32X attribute[133X
  
  [1X10.3-7 IsEmpty[101X
  
  [33X[1;0Y[29X[2XIsEmpty[102X( [3Xarg[103X ) [32X property[133X
  [6XReturns:[106X  [33X[0;10Y[9Xtrue[109X or [9Xfalse[109X[133X
  
  [1X10.3-8 Length[101X
  
  [33X[1;0Y[29X[2XLength[102X( [3Xarg[103X ) [32X attribute[133X
  
  [1X10.3-9 Position[101X
  
  [33X[1;0Y[29X[2XPosition[102X( [3Xarg1[103X, [3Xarg2[103X, [3Xarg3[103X ) [32X operation[133X
  
  [1X10.3-10 PositionSortedOp[101X
  
  [33X[1;0Y[29X[2XPositionSortedOp[102X( [3Xarg1[103X, [3Xarg2[103X ) [32X operation[133X
  
  [1X10.3-11 PositionSortedOp[101X
  
  [33X[1;0Y[29X[2XPositionSortedOp[102X( [3Xarg1[103X, [3Xarg2[103X, [3Xarg3[103X ) [32X operation[133X
  
