  
  
                                    [1X homalg [101X
  
  
     [1X A homological algebra meta-package for computable Abelian categories [101X
  
  
                                   2022.11-01
  
  
                                23 November 2022
  
  
                                Mohamed Barakat
  
                               Sebastian Gutsche
  
                             Markus Lange-Hegermann
  
  
  
  Mohamed Barakat
      Email:    [7Xmailto:mohamed.barakat@uni-siegen.de[107X
      Homepage: [7Xhttps://mohamed-barakat.github.io[107X
      Address:  [33X[0;14YWalter-Flex-Str. 3[133X
                [33X[0;14Y57072 Siegen[133X
                [33X[0;14YGermany[133X
  
  
  Sebastian Gutsche
      Email:    [7Xmailto:gutsche@mathematik.uni-siegen.de[107X
      Homepage: [7Xhttps://sebasguts.github.io[107X
      Address:  [33X[0;14YDepartment Mathematik[133X
                [33X[0;14YUniversität Siegen[133X
                [33X[0;14YWalter-Flex-Straße 3[133X
                [33X[0;14Y57072 Siegen[133X
                [33X[0;14YGermany[133X
  
  
  Markus Lange-Hegermann
      Email:    [7Xmailto:markus.lange-hegermann@hs-owl.de[107X
      Homepage: [7Xhttps://www.th-owl.de/eecs/fachbereich/team/markus-lange-hegermann/[107X
      Address:  [33X[0;14YMarkus Lange-Hegermann[133X
                [33X[0;14YHochschule Ostwestfalen-Lippe[133X
                [33X[0;14YLiebigstraße 87[133X
                [33X[0;14Y32657 Lemgo[133X
                [33X[0;14YGermany[133X
  
  
  
  -------------------------------------------------------
  [1XCopyright[101X
  [33X[0;0Y©  2007-2015  by Mohamed Barakat and Markus Lange-Hegermann This package may
  be  distributed  under  the  terms  and conditions of the GNU Public License
  Version 2 or (at your option) any later version.[133X
  
  
  -------------------------------------------------------
  [1XAcknowledgements[101X
  [33X[0;0YMax  Neunhöffer  not  only  taught  me  the  philosophy  of  object-oriented
  programming in [5XGAP4[105X, but also to what extent this philosophy is still unique
  among  programming  languages (--> [14XB.2[114X). He, Frank Lübeck, and Thomas Breuer
  patiently  answered  trillions  of  specific questions, even those I was too
  lazy  to  look  up  in  the  excellent  programming  tutorial. Without their
  continuous  and  tireless  help  and  advice,  not only this package but the
  [5Xhomalg[105X project as a whole would have remained on my todo list.[133X
  
  [33X[0;0YA  lot  of ideas that make up this package and the whole [5Xhomalg[105X project came
  out   of   intensive  discussions  with  Daniel  Robertz  during  our  early
  collaboration,  where  we  developed  our  philosophy  of a meta package for
  homological  algebra  and implemented it in [5XMaple[105X. This [5XMaple[105X package [5Xhomalg[105X
  is now part of the GAP package [5XRingsForHomalg[105X.[133X
  
  [33X[0;0YIn  the  fall  of  2007  I began collaborating with Simon Görtzen to further
  pursue  and  extend  these  ideas preparing the transition to [5XGAP4[105X. With his
  help [5Xhomalg[105X became an extendable multi-package project.[133X
  
  [33X[0;0YMax  Neunhöffer  convinced  me  to  use  his  wonderful  [5XIO[105X package to start
  communicating  with  external  computer algebra systems. This was crucial to
  remedy  the yet missing support for important rings in [5XGAP[105X. Max provided the
  first piece of code to access the computer algebra system [5XSingular[105X. This was
  the  starting point of the packages [5XHomalgToCAS[105X and [5XIO_ForHomalg[105X, which were
  further  abstracted  by Simon and myself enabling [5Xhomalg[105X to communicate with
  virtually any external (computer algebra) system.[133X
  
  [33X[0;0YThomas Bächler wrote the package [5XMapleForHomalg[105X to directly access [5XMaple[105X via
  its [5XC[105X-interface. It offers an alternative to the package [5XIO_ForHomalg[105X, which
  requires [5XMaple[105X's terminal interface [10Xcmaple[110X.[133X
  
  [33X[0;0YThe  basic support for [5XSage[105X was added by Simon, and the support for [5XSingular[105X
  was  initiated  by  Markus  Lange-Hegermann  and continued by him and Simon,
  while  Markus  Kirschmer  contributed  the  complete support for [5XMAGMA[105X. This
  formed  the  beginning of the [5XRingsForHomalg[105X package. Recently, Daniel added
  the support for [5XMacaulay2[105X.[133X
  
  [33X[0;0YMy  concerns  about  how  to  handle  the garbage collection in the external
  computer  algebra  systems  were  evaporated  with the idea of Thomas Breuer
  using  the so-called weak pointers in [5XGAP4[105X to keep track of all the external
  objects  that  became  obsolete  for  [5Xhomalg[105X.  This  idea  took  shape  in a
  discussion  with  him  and  Frank  Lübeck and finally found its way into the
  package [5XHomalgToCAS[105X.[133X
  
  [33X[0;0YMy  gratitude  to  all  with  whom  I  worked  together to develop extension
  packages  and  those  who  developed  their  own  packages within the [5Xhomalg[105X
  project  (-->  Appendix  [14XE[114X).  Without their contributions the package [5Xhomalg[105X
  would have remained a core without a body:[133X
  
  [30X    [33X[0;6YThomas                                                         Bächler
        (
        https://www.researchgate.net/scientific-contributions/50557632_Thomas_Baechler
        )[133X
  
  [30X    [33X[0;6YBarbara Bremer[133X
  
  [30X    [33X[0;6YThomas Breuer ([7Xhttp://www.math.rwth-aachen.de/~Thomas.Breuer/[107X)[133X
  
  [30X    [33X[0;6YAnna Fabiańska[133X
  
  [30X    [33X[0;6YSimon Görtzen ([7Xhttps://www.linkedin.com/in/simongoertzen/[107X)[133X
  
  [30X    [33X[0;6YMarkus Kirschmer ([7Xhttp://www.math.rwth-aachen.de/~Markus.Kirschmer/[107X)[133X
  
  [30X    [33X[0;6YMarkus                                                 Lange-Hegermann
        ([7Xhttps://www.th-owl.de/eecs/fachbereich/team/markus-lange-hegermann/[107X)[133X
  
  [30X    [33X[0;6YFrank Lübeck ([7Xhttp://www.math.rwth-aachen.de/~Frank.Luebeck/[107X)[133X
  
  [30X    [33X[0;6YMax Neunhöffer ([7Xhttps://www.arangodb.com/speakers/max-neunhoeffer/[107X)[133X
  
  [30X    [33X[0;6YDaniel Robertz ([7Xhttps://www.plymouth.ac.uk/staff/daniel-robertz[107X)[133X
  
  [33X[0;0YI  would  also like to thank Alban Quadrat for supporting the [5Xhomalg[105X project
  and  for all the wonderful discussions we had. At several places in the code
  I was happy to add the comment: [21XI learned this from Alban[121X.[133X
  
  [33X[0;0YMy  teacher  Wilhelm  Plesken  remains  an inexhaustible source of extremely
  broad and deep knowledge. Thank you for being such a magnificent person.[133X
  
  [33X[0;0YThis manual was created using the GAPDoc package of Max Neunhöffer and Frank
  Lübeck.[133X
  
  [33X[0;0YLast  but  not  least,  thanks  to  [13XMiriam[113X,  [13XJosef[113X, [13XJonas[113X, and [13XIrene[113X for the
  endless love and support.[133X
  
  [33X[0;0YMohamed Barakat[133X
  
  
  -------------------------------------------------------
  
  
  [1XContents (homalg)[101X
  
  1 [33X[0;0YIntroduction[133X
    1.1 [33X[0;0YWhat is the role of the [5Xhomalg[105X package in the [5Xhomalg[105X project?[133X
      1.1-1 [33X[0;0YPhilosophy[133X
      1.1-2 [33X[0;0Y[5Xhomalg[105X provides ...[133X
      1.1-3 [33X[0;0YBuilding upon the [5Xhomalg[105X package[133X
    1.2 [33X[0;0YThis manual[133X
  2 [33X[0;0YInstallation of the [5Xhomalg[105X Package[133X
  3 [33X[0;0YObjects[133X
    3.1 [33X[0;0YObjects: Category and Representations[133X
      3.1-1 IsHomalgObject
      3.1-2 IsHomalgStaticObject
      3.1-3 IsFinitelyPresentedObjectRep
      3.1-4 IsStaticFinitelyPresentedObjectOrSubobjectRep
      3.1-5 IsStaticFinitelyPresentedObjectRep
      3.1-6 IsStaticFinitelyPresentedSubobjectRep
    3.2 [33X[0;0YObjects: Constructors[133X
      3.2-1 Subobject
    3.3 [33X[0;0YObjects: Properties[133X
      3.3-1 IsFree
      3.3-2 IsStablyFree
      3.3-3 IsProjective
      3.3-4 IsProjectiveOfConstantRank
      3.3-5 IsInjective
      3.3-6 IsInjectiveCogenerator
      3.3-7 FiniteFreeResolutionExists
      3.3-8 IsReflexive
      3.3-9 IsTorsionFree
      3.3-10 IsArtinian
      3.3-11 IsTorsion
      3.3-12 IsPure
      3.3-13 IsCohenMacaulay
      3.3-14 IsGorenstein
      3.3-15 IsKoszul
      3.3-16 HasConstantRank
      3.3-17 ConstructedAsAnIdeal
    3.4 [33X[0;0YObjects: Attributes[133X
      3.4-1 TorsionSubobject
      3.4-2 TheMorphismToZero
      3.4-3 TheIdentityMorphism
      3.4-4 FullSubobject
      3.4-5 ZeroSubobject
      3.4-6 EmbeddingInSuperObject
      3.4-7 SuperObject
      3.4-8 FactorObject
      3.4-9 UnderlyingSubobject
      3.4-10 NatTrIdToHomHom_R
      3.4-11 Annihilator
      3.4-12 EndomorphismRing
      3.4-13 UnitObject
      3.4-14 RankOfObject
      3.4-15 ProjectiveDimension
      3.4-16 DegreeOfTorsionFreeness
      3.4-17 Grade
      3.4-18 PurityFiltration
      3.4-19 CodegreeOfPurity
      3.4-20 HilbertPolynomial
      3.4-21 AffineDimension
      3.4-22 ProjectiveDegree
      3.4-23 ConstantTermOfHilbertPolynomialn
      3.4-24 ElementOfGrothendieckGroup
      3.4-25 ChernPolynomial
      3.4-26 ChernCharacter
    3.5 [33X[0;0YObjects: Operations and Functions[133X
      3.5-1 CurrentResolution
      3.5-2 UnderlyingObject
      3.5-3 Saturate
  4 [33X[0;0YMorphisms[133X
    4.1 [33X[0;0YMorphisms: Categories and Representations[133X
      4.1-1 IsHomalgMorphism
      4.1-2 IsHomalgStaticMorphism
      4.1-3 IsHomalgEndomorphism
      4.1-4 IsMorphismOfFinitelyGeneratedObjectsRep
      4.1-5 IsStaticMorphismOfFinitelyGeneratedObjectsRep
    4.2 [33X[0;0YMorphisms: Constructors[133X
    4.3 [33X[0;0YMorphisms: Properties[133X
      4.3-1 IsMorphism
      4.3-2 IsGeneralizedMorphismWithFullDomain
      4.3-3 IsGeneralizedEpimorphism
      4.3-4 IsGeneralizedMonomorphism
      4.3-5 IsGeneralizedIsomorphism
      4.3-6 IsOne
      4.3-7 IsIdempotent
      4.3-8 IsMonomorphism
      4.3-9 IsEpimorphism
      4.3-10 IsSplitMonomorphism
      4.3-11 IsSplitEpimorphism
      4.3-12 IsIsomorphism
      4.3-13 IsAutomorphism
    4.4 [33X[0;0YMorphisms: Attributes[133X
      4.4-1 Source
      4.4-2 Range
      4.4-3 CokernelEpi
      4.4-4 CokernelNaturalGeneralizedIsomorphism
      4.4-5 KernelSubobject
      4.4-6 KernelEmb
      4.4-7 ImageSubobject
      4.4-8 ImageObjectEmb
      4.4-9 ImageObjectEpi
      4.4-10 MorphismAid
      4.4-11 InverseOfGeneralizedMorphismWithFullDomain
      4.4-12 DegreeOfMorphism
    4.5 [33X[0;0YMorphisms: Operations and Functions[133X
      4.5-1 ByASmallerPresentation
  5 [33X[0;0YElements[133X
    5.1 [33X[0;0YElements: Category and Representations[133X
      5.1-1 IsHomalgElement
      5.1-2 IsElementOfAnObjectGivenByAMorphismRep
    5.2 [33X[0;0YElements: Constructors[133X
    5.3 [33X[0;0YElements: Properties[133X
      5.3-1 IsZero
      5.3-2 IsCyclicGenerator
      5.3-3 IsTorsion
    5.4 [33X[0;0YElements: Attributes[133X
      5.4-1 Annihilator
    5.5 [33X[0;0YElements: Operations and Functions[133X
      5.5-1 in
  6 [33X[0;0YComplexes[133X
    6.1 [33X[0;0YComplexes: Category and Representations[133X
      6.1-1 IsHomalgComplex
      6.1-2 IsComplexOfFinitelyPresentedObjectsRep
      6.1-3 IsCocomplexOfFinitelyPresentedObjectsRep
    6.2 [33X[0;0YComplexes: Constructors[133X
      6.2-1 HomalgComplex
      6.2-2 HomalgCocomplex
    6.3 [33X[0;0YComplexes: Properties[133X
      6.3-1 IsSequence
      6.3-2 IsComplex
      6.3-3 IsAcyclic
      6.3-4 IsRightAcyclic
      6.3-5 IsLeftAcyclic
      6.3-6 IsGradedObject
      6.3-7 IsExactSequence
      6.3-8 IsShortExactSequence
      6.3-9 IsSplitShortExactSequence
      6.3-10 IsTriangle
      6.3-11 IsExactTriangle
    6.4 [33X[0;0YComplexes: Attributes[133X
      6.4-1 BettiTable
      6.4-2 FiltrationByShortExactSequence
    6.5 [33X[0;0YComplexes: Operations and Functions[133X
      6.5-1 Add
      6.5-2 ByASmallerPresentation
  7 [33X[0;0YChain Morphisms[133X
    7.1 [33X[0;0YChainMorphisms: Categories and Representations[133X
      7.1-1 IsHomalgChainMorphism
      7.1-2 IsHomalgChainEndomorphism
      7.1-3 IsChainMorphismOfFinitelyPresentedObjectsRep
      7.1-4 IsCochainMorphismOfFinitelyPresentedObjectsRep
    7.2 [33X[0;0YChain Morphisms: Constructors[133X
      7.2-1 HomalgChainMorphism
    7.3 [33X[0;0YChain Morphisms: Properties[133X
      7.3-1 IsMorphism
      7.3-2 IsGeneralizedMorphismWithFullDomain
      7.3-3 IsGeneralizedEpimorphism
      7.3-4 IsGeneralizedMonomorphism
      7.3-5 IsGeneralizedIsomorphism
      7.3-6 IsOne
      7.3-7 IsMonomorphism
      7.3-8 IsEpimorphism
      7.3-9 IsSplitMonomorphism
      7.3-10 IsSplitEpimorphism
      7.3-11 IsIsomorphism
      7.3-12 IsAutomorphism
      7.3-13 IsGradedMorphism
      7.3-14 IsQuasiIsomorphism
    7.4 [33X[0;0YChain Morphisms: Attributes[133X
      7.4-1 Source
      7.4-2 Range
    7.5 [33X[0;0YChain Morphisms: Operations and Functions[133X
      7.5-1 ByASmallerPresentation
  8 [33X[0;0YBicomplexes[133X
    8.1 [33X[0;0YBicomplexes: Category and Representations[133X
      8.1-1 IsHomalgBicomplex
      8.1-2 IsBicomplexOfFinitelyPresentedObjectsRep
      8.1-3 IsBicocomplexOfFinitelyPresentedObjectsRep
    8.2 [33X[0;0YBicomplexes: Constructors[133X
      8.2-1 HomalgBicomplex
    8.3 [33X[0;0YBicomplexes: Properties[133X
      8.3-1 IsBisequence
      8.3-2 IsBicomplex
      8.3-3 IsTransposedWRTTheAssociatedComplex
    8.4 [33X[0;0YBicomplexes: Attributes[133X
      8.4-1 TotalComplex
      8.4-2 SpectralSequence
    8.5 [33X[0;0YBicomplexes: Operations and Functions[133X
      8.5-1 UnderlyingComplex
      8.5-2 ByASmallerPresentation
  9 [33X[0;0YBigraded Objects[133X
    9.1 [33X[0;0YBigradedObjects: Categories and Representations[133X
      9.1-1 IsHomalgBigradedObject
      9.1-2 IsHomalgBigradedObjectAssociatedToAnExactCouple
      9.1-3 IsHomalgBigradedObjectAssociatedToAFilteredComplex
      9.1-4 IsHomalgBigradedObjectAssociatedToABicomplex
      9.1-5 IsBigradedObjectOfFinitelyPresentedObjectsRep
    9.2 [33X[0;0YBigraded Objects: Constructors[133X
      9.2-1 HomalgBigradedObject
      9.2-2 AsDifferentialObject
      9.2-3 DefectOfExactness
    9.3 [33X[0;0YBigraded Objects: Properties[133X
      9.3-1 IsEndowedWithDifferential
      9.3-2 IsStableSheet
    9.4 [33X[0;0YBigraded Objects: Operations and Functions[133X
      9.4-1 ByASmallerPresentation
  10 [33X[0;0YSpectral Sequences[133X
    10.1 [33X[0;0YSpectralSequences: Categorie and Representations[133X
      10.1-1 IsHomalgSpectralSequence
      10.1-2 IsHomalgSpectralSequenceAssociatedToAnExactCouple
      10.1-3 IsHomalgSpectralSequenceAssociatedToAFilteredComplex
      10.1-4 IsHomalgSpectralSequenceAssociatedToABicomplex
      10.1-5 IsSpectralSequenceOfFinitelyPresentedObjectsRep
      10.1-6 IsSpectralCosequenceOfFinitelyPresentedObjectsRep
    10.2 [33X[0;0YSpectral Sequences: Constructors[133X
      10.2-1 HomalgSpectralSequence
    10.3 [33X[0;0YSpectral Sequences: Attributes[133X
      10.3-1 GeneralizedEmbeddingsInTotalObjects
      10.3-2 GeneralizedEmbeddingsInTotalDefects
    10.4 [33X[0;0YSpectral Sequences: Operations and Functions[133X
      10.4-1 ByASmallerPresentation
  11 [33X[0;0YFunctors[133X
    11.1 [33X[0;0YFunctors: Category and Representations[133X
      11.1-1 IsHomalgFunctor
      11.1-2 IsHomalgFunctorRep
    11.2 [33X[0;0YFunctors: Constructors[133X
      11.2-1 CreateHomalgFunctor
      11.2-2 InsertObjectInMultiFunctor
      11.2-3 RightSatelliteOfCofunctor
      11.2-4 LeftSatelliteOfFunctor
      11.2-5 RightDerivedCofunctor
      11.2-6 LeftDerivedFunctor
      11.2-7 ComposeFunctors
    11.3 [33X[0;0YFunctors: Attributes[133X
      11.3-1 NameOfFunctor
      11.3-2 OperationOfFunctor
      11.3-3 Genesis
      11.3-4 ProcedureToReadjustGenerators
    11.4 [33X[0;0YBasic Functors[133X
      11.4-1 functor_Kernel
      11.4-2 functor_DefectOfExactness
    11.5 [33X[0;0YTool Functors[133X
    11.6 [33X[0;0YOther Functors[133X
    11.7 [33X[0;0YFunctors: Operations and Functions[133X
      11.7-1 InstallFunctor
      11.7-2 InstallDeltaFunctor
  12 [33X[0;0YExamples[133X
    12.1 [33X[0;0YExtExt[133X
    12.2 [33X[0;0YPurity[133X
    12.3 [33X[0;0YTorExt-Grothendieck[133X
    12.4 [33X[0;0YTorExt[133X
  A [33X[0;0YThe Mathematical Idea behind [5Xhomalg[105X[133X
  B [33X[0;0YDevelopment[133X
    B.1 [33X[0;0YWhy was [5Xhomalg[105X discontinued in [5XMaple[105X?[133X
    B.2 [33X[0;0YWhy [5XGAP4[105X?[133X
      B.2-1 [33X[0;0Y[5XGAP[105X is free and open software[133X
      B.2-2 [33X[0;0Y[5XGAP[105X has an area of expertise[133X
      B.2-3 [33X[0;0Y[5XGAP4[105X can communicate[133X
      B.2-4 [33X[0;0Y[5XGAP4[105X is a [13Xmathematical[113X object-oriented programming language[133X
      B.2-5 [33X[0;0Y[5XGAP4[105X packages are easily extendible[133X
    B.3 [33X[0;0YWhy not [5XSage[105X?[133X
    B.4 [33X[0;0YHow does [5Xhomalg[105X compare to [5XSage[105X?[133X
      B.4-1 [33X[0;0YThey differ in objectives and scale[133X
      B.4-2 [33X[0;0YThey differ in the programming language[133X
      B.4-3 [33X[0;0YThey differ in the way they communicate with the outer world[133X
  C [33X[0;0YLogic Subpackages[133X
    C.1 [33X[0;0Y[5XLIOBJ[105X: Logical Implications for Objects of Abelian Categories[133X
    C.2 [33X[0;0Y[5XLIMOR[105X: Logical Implications for Morphisms of Abelian Categories[133X
    C.3 [33X[0;0Y[5XLICPX[105X: Logical Implications for Complexes in Abelian Categories[133X
  D [33X[0;0YDebugging [5Xhomalg[105X[133X
    D.1 [33X[0;0YIncrease the assertion level[133X
  E [33X[0;0YThe Core Packages and the Idea behind their Splitting[133X
    E.1 [33X[0;0YThe 6=2+4 split[133X
      E.1-1 [33X[0;0YLogically independent[133X
      E.1-2 [33X[0;0YBlack boxes[133X
      E.1-3 [33X[0;0YSumming up[133X
    E.2 [33X[0;0YThe 4=1+1+1+1 split[133X
      E.2-1 [33X[0;0Y[5XHomalgToCAS[105X[133X
      E.2-2 [33X[0;0Y[5XIO_ForHomalg[105X and Alternatives[133X
      E.2-3 [33X[0;0Y[5XRingsForHomalg[105X[133X
      E.2-4 [33X[0;0YYour own [5XRingsForHomalg[105X[133X
      E.2-5 [33X[0;0Y[5XExamplesForHomalg[105X[133X
      E.2-6 [33X[0;0YDocumentation[133X
      E.2-7 [33X[0;0YCrediting[133X
      E.2-8 [33X[0;0YStability[133X
  F [33X[0;0YOverview of the [5Xhomalg[105X Package Source Code[133X
    F.1 [33X[0;0YThe Basic Objects[133X
    F.2 [33X[0;0YThe High Level Homological Algorithms[133X
    F.3 [33X[0;0YLogical Implications for [5Xhomalg[105X Objects[133X
  
  
  [32X
