## CHANGES to the 'XMod' package
## 2.94 -> 2.95 (10/07/2025)
* (10/07/25) added PreXModWithObjectsByBoundaryAndAction
* (30/06/25) make the new groupoids 1.77 a prerequisite and revise material
on double groupoids to agree with the changes in groupoids
## 2.93 -> 2.94 (08/07/25)
* (08/07/25) temporary fix to work with the recently released groupoids 1.77
## 2.92 -> 2.93 (27/04/2025)
* (27/04/25) added sub-crossed square and sub-cat2-group operations
* (25/04/25) simplified the construction of crossed pairings so that
files map2arg.g{d,i} can be removed
* (20/12/24) changed the examples of induced crossed modules in section 7.2
* (17/12/24) implemented (Inner)ActorCat1Group, fixing issue #144
* (20/11/24) added AutomorphismPermGroup method for cat1-groups
renamed PermAutomorphismAsXModMorphism as
PermAutomorphismAs2dGroupMorphism and added cat1-group method
added WhiteheadRegularGroup and WhiteheadGroupIsomorphism
removed the unused CompositeDerivation (= WhiteheadProduct)
removed the unused (List)InverseDerivations
renamed WhiteheadGroupGeneratingDerivations as ...UpMappings
added WhiteheadGroupInverseIsomorphism
fixed error in CrossedPairingByDerivations
## 2.91 -> 2.92 (23/01/2024)
* (11/10/23) methods for WhiteheadXMod etc for xmods which are not perm
* (16/02/23) now using the NC version of PreImagesRepresentative
## 2.89 -> 2.91 (16/02/2023)
* (16/02/23) revised tst/extra/d24.tst so that it works with option -A
* (09/02/23) added a chapter on double groupoids with operations
EnhancedBasicDoubleGroupoid, DoubleGroupoidWithZeroBoundary
* (05/02/23) added PreXModWithTrivialRange
## 2.88 -> 2.89 (04/02/2023)
* (01/02/23) added RegularActionHomomorphism(Object/2DimensionalGroup)
* (23/12/22) changed email address and other personal details
* (24/08/22) manual: documented DerivationImage;
corrected CrossDiagonalActions
## 2.86 -> 2.88 (28/04/2022)
* (27/04/22) introduced Size2d for 2d-objects and Size3d for 3d-objects
added the Arvasi/Odabas/Wensley paper to the list of references
## 2.85 -> 2.86 (14/03/2022)
* (14/03/22) moved d24.tst to tst/failing temporarily
## 2.84 -> 2.85 (12/03/2022)
* (12/03/22) commented out some tests that failed in gapdev
* (24/11/21) NaturalHomomorphism -> NaturalHomomorphismByNormalSubgoup
## 2.83 -> 2.84 (15/11/2021)
* (15/11/21) corrected address for CDW:
https://github.com/cdwensley
* (08/04/21) Switch CI to use GitHub Actions
## 2.82 -> 2.83 (17/02/2021)
* (17/02/21) added functions for quasi-isomorphisms - manual section 3.5
* (26/10/20) corrected \^ for morphisms of 2dimensional groups
* (25/10/20) added examples/cpcpcp.g constructing 23 cat2-groups on (Cp)^3
## 2.81 -> 2.82 (23/10/2020)
* (22/10/20) revised IsomorphismPreCat1Groups
* (19/10/20) added IsSymmetric2DimensionalGroup
* (25/08/20) removed perm groups as range in KernelCokernelXMod
* (07/08/20) added the property IsSubEndoMapping to util.{gd,gi}
* (20/07/20) revised the function AllXModsUpToIsomorphism etc.
* (15/06/20) renamed/revised PreXModRecordOfPreCat1Group (and conversely)
* (10/06/20) restructured cat1data.g so that the numbering agrees with HAP
* (30/05/20) added HAP chapter to the manual plus XMod <-> HAP functions
## 2.79 -> 2.81 (25/05/2020)
* (24/05/20) added AllCat2GroupsWithFixedUp(AndLeftRange)
* (10/05/20) split gp3objmap.tst into gp3xs.tst and gp3cat2.tst
added operation AllCat2GroupMatrix
* (08/05/20) added DirectProductOp method for PreCat2Groups
added PreCat2GroupMorphismByGroupHomomorphisms method
## 2.77 -> 2.79 (04/05/2020)
* (04/05/20) added operation LoopClasses to go with (All)LoopsXMod
* (03/05/20) reinstalling the package after hard disc replacement
* (19/04/20) added operation DisplayLeadMaps for a HigherDimensionalDomain
fixed an error in AllCat2GroupsWithImagesUpToIsomorphism
* (16/04/20) fixed an error in the function GroupGroupoid
* (03/04/20) added fields .symm1 and .siso1 to CatnGroupNumbers
* (02/04/20) revised IsomorphismPreCat1Groups
* (27/03/20) IsPreCat1GroupByEndomorphisms (ditto CatnGroup)
-> IsPreCat1GroupWithIdentityEmbedding
(IsomorphismTo)EndomorphismCat1Group
-> IsomorphicPreCat1GroupWithIdentityEmbedding
* (12/03/20) now SmallerDegreePermutationRepresentation2DimensionalGroup in
place of SmallerDegreePerm2DimensionalDomain
* (06/03/20) now running under GAP 4.11.0
* (02/03/20) fixed issue 41, (Direct/Co)Product for more than two objects
* (01/03/20) corrected DiagonalCat1Group
* (29/02/20) added SubdiagonalCat1Group and IsSubXMod, IsSub***
* (30/01/20) added tests on kernels in IsomorphismCat1Groups - valid??
* (14/01/20) fixed IdentityMapping for cat2-groups and catn-groups
* (10/01/20) revised CatnGroupNumbers fields for crossed squares & cat2-groups
* (24/11/19) added DirectProduct for cat1-groups (& revised for xmods)
## 2.74 -> 2.77 (17/11/2019)
* (17/11/19) fixed XModByGroupOfAutomorphisms and updated manual
* (16/11/19) corrected Transpose3DimensionalGroup for cat2-groups
* (12/11/19) reverted need for a cat2-group to have a diagonal cat1-group
## 2.73 -> 2.74 (11/10/2019)
* (09/10/19) Cat1GroupOfXMod now a record storing embeddings of S,R in G
* (01/10/19) added second example in section 8.2.14
* (10/09/19) added methods for (Pre)CrossedSquareBy(Pre)XMods
* (09/09/19) revised CrossedSquare consructors to use diag, not the action
* (06/09/19) added allcat2pos to CatnGroupLists(G)
* (03/09/19) major revision: PreCat2Group and DetermineRemainingCat1Groups
* (02/09/19) replaced IsEndomorphismCat1Group by IsCat1GroupByEndomorphisms
* (27/08/19) added AllCat3Groups, AllCat3GroupTriples, AllCat3GroupsNumber
* (14/08/19) added AllCat1GroupMorphisms and simplified AllCat2GroupMorphisms
* (13/08/19) changes to gp{2,3,4}map.gi to make cat2-xs.tst work for the paper
* (07/08/19) functions for cat3-groups in gp4obj.g{d,i}
* (30/07/19) modified induced.tst and isoclinic.tst to avoid gapdev diffs
* (26/07/19) added .pairs and .fams to CatnGroupLists record
* (17/07/19) modified .travis.yml in line with Max' changes in Utils
* (17/07/19) added operation AllCat2GroupFamilies and updated the manual
* (16/07/19) added attribute record CatnGroupNumbers for a group
* (11/07/19) added new method for IsPreCat2GroupMorphism
* (17/06/19) revised AllCat{1,2}... functions using iterators in utils-0.64
* (10/06/19) complete rewrite of IsomorphismCat2Groups
* (15/05/19) new AllCat{1,2}GroupsIterator, AllCat{1,2}GroupsNumber
* (10/05/19) added in new functions from Alper for AllCat2Groups (up to iso)
* (18/04/19) reorganised all .tst files into /tst/manual/ and /tst/extra/
* (11/04/19) corrected UnionOfPiecesOp for prexmods with objects
* (09/04/19) added names and examples of crossed pairing functions to manual
* (13/03/19) added initial implementation of group groupoids (manual 2.8)
## 2.72 -> 2.73 (04/03/2019)
* (04/03/19) Cat2GroupOfCrossedSquare now giving results again
crossed pairings now consistently maps : N x M -> L
* (16/02/19) added License field in PackageInfo.g
* (08/12/18) added InducedXModByBijection, InducedXModByCoproduct and
renamed SurjectiveInducedXMod, InclusionInducedXModByCopower
* (06/12/18) added a CoproductXMod method for a list with more than two xmods
* (05/12/18) added CrossedSquareByXModSplitting
* (03/12/18) add CrossedSquareByAutomorphismGroup, CrossedPairingByConjugators
* (01/12/18) added method for IsCrossedSquare
* (28/11/18) new version of 2-argument functions in map2arg.{gd,gi}
* (26/11/18) added CrossedSquareByPullback and XModByPullback
* (21/11/18) added PrincipalCrossedPairing
* (19/11/18) added IsNormalSub2DimensionalDomain and used this when calling
CrossedSquareByNormalSubXMod
* (15/11/18) renamed CrossedSquareMorphismByMorphisms
as CrossedSquareMorphismByXModMorphisms
and added CrossedSquareMorphismByGroupHomomorphisms;
ditto for Cat2GroupMorphisms
XModMorphismByHoms -> XModMorphismByGroupHomomorphisms
* (14/11/18) Cat1Morphism -> Cat1GroupMorphism, ditto Cat2Morphism, etc.
removed IsomorphismSmallPermGroup, NiceObject, etc from util.*
* (08/11/18) added KernelCokernelXMod, fixing issue #34
* (07/11/18) XModByAutomorphismGroup is now an attribute, not a global fn.
* (07/11/18) fixed problem with Cat2GroupOfCrossedSquare
* (06/11/18) added special case of InducedXMod when iota is bijective
## 2.69 -> 2.72 (16/09/2018)
* (10/09/18) replaced PrintOneItemPerLine(L); with Perform(L,Display);
* (02/09/18) added CrossedPairingByXModAction, CrossedSquareByNormalSubXMod
* (30/08/18) PreCat2GroupOfPreCrossedSquare revised : q8xscat2.tst, d24.tst
* (07/08/18) added PreCat2GroupByPreCat1Groups and other changes to gp3obj.*
* (01/08/18) fixed issue #24 and added xtst/cat1data.tst
* (30/07/18) fixed issue #9
## 2.68 -> 2.69 (20/07/2018)
* (12/07/18) added operations InducedXModFromTrivialSource/Range
* (05/07/18) major revision of InclusionInducedXModByCopower
* (29/06/18) added method for IsCentralExtension2DimensionalGroup
* (28/06/18) added operation DisplacementGroup; changed DisplacementSubgroup
* (17/05/18) corrected SinglePiecePreXModWithObjects in the discrete case
## 2.67 -> 2.68 (01/05/2018)
* (30/04/18) made tests more robust; moved coprod.tst to /xtst
## 2.66 -> 2.67 (29/04/2018)
* (23/04/18) avoid use of FactorGroup - just use Image( nat )
* (19/04/18) replace Image(f,x) by ImageElm(f,x) throughout
## 2.65 -> 2.66 (12/04/2018)
* (12/04/18) added LoopsXMod functions: apps.{gd,gi,xml}, loops.{g,tst}
## 2.64 -> 2.65 (21/03/2018)
* (18/03/18) remove some of the temporary synonyms (09/08/17)
* (13/02/18) CompositeDerivation/Section now WhiteheadProduct
SectionByImages now SectionByHomomorphism
added IdentityDerivation; IdentitySection; WhiteheadOrder
* (12/02/18) AllOrRegular now DerivationClass; revised PrincipalDerivations
* (10/01/12) converted LaTeX entities back in to newcommands
* (09/01/18) now using AutoDoc to build the manual
* (15/12/17) removed examples/; added expt/; *.tst files in xtst/
## 2.63 -> 2.64 (30/11/2017)
* (29/11/17) fixed tests to work with both 4r8 and dev in 3 options
* (23/11/17) removed attribute AutoGroup (=Range(XModAction)) for xmods
* (22/11/17) added operations SinglePiecePreXModWithObjects(NC)
* (16/11/17) added Root2dGroup for prexmods with objects
* (17/10/17) ImageElmXModAction now working for xmods of groupoids
* (04/10/17) added operation ImageElmXModAction
* (01/10/17) renamed test files and made them independent
* (27/09/17) added tst/testextra.g, tst/allxmods.xtst, tst/cat1mor.xtst
## 2.61 -> 2.63 (26/09/2017)
* (26/09/17) added a number of Types and modified Objectify statements
removed Up2DimensionalMappingObj
* (24/08/17) changed the name of Murat's university
* (09/08/17) in order to keep XModAlg-1.12 working, added synonyms
Is2dDomain for Is2DimensionalDomain,
PreCat1ByTailHeadEmbedding for PreCat1Obj,
PreCat1ByEndomorphisms for PreCat1GroupByEndomorphisms
PreCat1ByPreXMod for PreCat1GroupOfPreXMod
IsGeneral2dMapping for IsGeneral2DimensionalMapping
and Kernel2dMapping for Kernel2DimensionalMapping
## 2.59 -> 2.61 (07/08/2017)
* (07/08/17) Gpd changed to groupoids in list of required packages
* (07/08/17) testall.g now calls TestDirectory; test files renamed
* (07/08/17) temporarily renamed 08-gpd2obj.tst and 11-gpnobjmap.tst
so that they do not get tested by TestDirectory("tst")
* (21/07/17) replaced PreXModIsomorphismByIsomorphisms by the more general
IsomorphismByIsomorphisms; then functions such as
IsomorphismPerm2DimensionalGroup rewritten to use it.
* (20/07/17) added IsomorphismByIsomorphisms for pre1-cat-groups
* (20/07/17) Removed duplication in 'Of' and 'By' operations
* (17/07/17) new functions added by Alper for crossed square <-> cat2-group:
ConjugationActionForCrossedSquare;
ElementsRelationsForSemidirectProduct
* (14/06/17) added methods for String, ViewString, PrintString
* (09/05/17) `dom2d3d.g{d,i}` renamed `dom2dnd.g{d,i}`
hdim-morphisms now expect [ src, rng, list of maps ]
PreCatn(Mapping)Dimension now HigherDimension
added attribute VertexGroups for HigherDimensionalGroups
* (08/05/17) Removed lots of 3Dim stuff since HigherDim stuff is better
* (05/05/17) AllCat1Groups\* -> AllCat1DataGroups\*
* (04/05/17) Alper add catn-morphism functions in `gpnmor.g{d,i}`
* (29/04/17) added lines to `makedoc.g` to allow for xymatrix commands
* (24/04/17) 2d<anything> becomes 2Dimensional<anything> (except Object2d)
* (22/04/17) Alper added `lib/gpnobj.gd`, `lib/gpnobj.gi`, `tst/gpnobjmap.tst`
* (10/04/17) Alper added a number of functions for cat2-groups and morphisms
Replaced XPairing with CrossedPairing
* (04/04/17) added CoproductInfo for coproducts
FactorXMod now FactorPreXMod (ditto NaturalMorphisms)
* (27/03/17) added Is2dGroupMorphismData and modified construction functions
Method for IsNormal now applies to precrossed modules
added PeifferSub2dGroup
* (24/03/17) added operation DiagonalCat1 and example S3xS3 => S3
* (22/03/17) added operation CoproductXMod and files `coprod.g`, `coprod.tst`
## 2.58 -> 2.59 (21/03/2017)
* (21/03/17) added property IsEndomorphismPreCat1
modified IsomorphismPerm2dGroup for PreCat1 objects
* (14/11/16) "first author" -> "second author" in `manual.xml` (issue #4)
## 2.56 -> 2.58 (02/11/2016)
* (18/10/16) now using bibliography file `bib.xml` of type `bibxmlext.dtd`
* (13/10/16) changed package releases to <
https://gap-packages.github.io/xmod>
* (24/03/16) added files `hap.gd`, `hap.gi`
* (16/03/16) edited `utils.tst` to remove functions transferred to Utils
## 2.51 -> 2.56 (08/03/2016)
* (23/02/16) remove functions from `util.g{d/i}` now in Utils; require Utils
* (18/02/16) removed date/version info from file headers
* (16/02/16) require Gpd >= 1.42;
## 2.45 -> 2.51 (09/02/2016)
* (08/02/16) necessary changes to test files to fix new output errors
## 2.44 -> 2.45 (29/12/2015)
* (29/12/15) fixed changes in output from `\*.tst` files
## 2.42 -> 2.44 (13/11/2015)
* (11/11/15) renamed Rank and MiddleLength and now for p-groups only
* (10/11/15) changes examples in tests to avoid repeated variable names
* (09/11/15) XPair -> XPairing, etc.
* (08/11/15) IsomorphismPermPre(XMod/Cat1) -> IsomorphismPerm2dGroup, etc.
* (07/11/15) Revised manual, chapter 7, and isoclinic.tst
* (06/11/15) IsStemGroup & IsStemXMod -> IsStemDomain etc.
* (04/11/15) RestrictionMappingGroups -> GeneralRestgrictedMapping
* (01/11/15) `makedocrel.g` : added MathJax; changed "doc" to XModDoc
* (20/10/15) moved code from FactorXMod to NaturalMorphismByNormalSubXMod
corrected formulae in Displacement and DisplacementSubgroup
* (19/10/15) revised Isoclinism for xmods; IsoAllXMods -> AllXModsUpToIso..
* (16/10/15) changed all occurrences of XSq to CrossedSquare
* (15/10/15) fixed Iterator bug in Isoclinism for groups
* (13/10/15) CentralQuotient now a crossed module or a crossed square
added LeftRightMorphism and UpDownMorphism for crossed squares
* (07/10/15) AllXMods and AllPreXMods now global functions
added property IsStemXMod
* (06/10/15) renamed IsIsomorphicXMod as IsomorphismXMods;
fixed the call to IsXMod in PreXModObj
* (05/10/15) added Centralizer and Normalizer methods for crossed modules
* (02/10/15) added ExternalSetXMod
* (01/10/15) added operation Displacement
* (28/09/15) added AllStemGroupFamilies and Set various Names
* (26/09/15) added NaturalHomomorphismByNormalSubXMod
* (24/09/15) added CrossActionSubgroup
* (23/09/15) removed last occurrences of AllIsomorphisms
* (22/09/15) added functions for isoclinism of groups
* (18/09/15) processed a number of properties in the isoclinic files
* (17/09/15) added example in manual subsection 2.1.4.
* (15/09/15) methods for InnerMorphism, ActorXMod, CentreXMod, etc.
now specified only for permutation crossed modules
* (24/08/15) major edits to `README`, including GitHub issues link
## 2.41 -> 2.42 (24/08/2015)
* (24/08/15) made version to be moved from Bitbucket to GitHub
* (20/07/15) fixed bug in IsomorphismPcPreCat1 reported by Charles Melville
## 2.32 -> 2.41 (05/06/2015)
* (05/06/15) `gpd2obj.gd` changed to reflect changes in package Gpd
## 2.31 -> 2.32 (26/02/2015)
* (26/02/15) reverted AllInducedXMods(Cat1s) to global functions
* (03/02/15) added properties IsPreXModDomain and IsPreCat1Domain
which are meant to apply to both group and algebra cases
* (02/02/15) took out all MultiplicativeElementWithTuple's etc.
and Multiplicative2dElement's etc.
* (29/01/15) made copies of `dom2d3d,g{d,i}` and `gp2obj.g{d,i}`
before embarking on a major rewrite of the category structure:
specifically, changing lots of '2dDomain's into '2dGroup's
## 2.26 -> 2.31 (17/12/2014)
* (17/12/14) moved package home page to <pages.bangor.ac.uk/~mas023/chda/xmod/>
* (08/11/14) created BitBucket repository for 'XMod'
## 2.22 -> 2.26 (26/11/2013)
* (26/11/13) minor mod to WhiteheadTransMonoid to fix `gp2up.tst` output
* (03/11/13) fixed errors in `cat1data.g` reported by Van Luyen Le.
* (15/10/13) fixed error in Cat1MorphismByXModMorphism.
* (03/10/13) completed work on groups of order [64..70] in `cat1data.g`
* (02/10/13) added operation CollectPartsAlreadyDone.
* (01/10/13) added operation PreCat1IsomorphismByIsomorphisms.
* (17/08/13) fixed bug in PermCat1Select sent by Van Luyen Le
* (26/03/13) put groups of order 64 back into `cat1data.g`
* (05/02/13) rewrite of `testall.g` following Alex K's wedderga example
## 2.19 -> 2.22 (25/01/2013)
* (25/01/13) Minor change to test file output to avoid problems in tests.
* (09/01/13) Changed PackageWWWHome, using "gap4" rather than "gap4r5".
Unable to fix problems related to changes in `lib/ghom.gi`,
so removed `gpd2obj.tst` from the set of standard tests:
the problem is with changes to GroupGeneralMappingByImages.
* (26/09/12) Moved functions to the new `cat1data.gd`, `cat1data.gi`.
* (21/09/12) Edited test files to reflect recent changes
* (12/07/12) Changed the format and rebuilt the data file `cat1data.g` :-
it is now assumed that the SmallGroups library is used.
Extended `cat1data.g` from order 47 to most of order 64.
Major revision of AllCat1s, MakeAllCat1s, Cat1Select
* (04/07/12) Added AllCat1s and IsomorphismPreCat1s (from GAP3 version).
Removed batch of functions from `util.g{d,i}` involving
EndomorphismClasses, IdempotentImages, etc.
Replaced their use in AllCat1s with calls to GQuotients.
## 2.18 -> 2.19 (09/06/2012)
* (08/06/12) Following the replacement of IdentitySubgroup by TrivialSubgroup
in Gpd, renamed IdentitySubXMod by TrivialSubXMod, etc.
All calls of GroupHomomorphismByImagesTriv returned to
GroupHomomorphismByImages (see item dated 30/04/08)
* (07/06/12) Renamed special Display for lists as PrintListOneItemPerLine following email f
rom Max Horn
## 2.17 -> 2.18 (23/04/2012)
* (23/04/12) added autpgrp as a needed package
* (26/01/12) replaced XModActedUpon by AutomorphismDomain in `gp2act.g{d,i}`
* (25/01/12) fixed error in XModByGroupOfAutomorphisms (oneG now oneP)
* (10/01/12) updated to 2012; corrected URLs in `intro.xml`
* (15/12/11) now requires version 1.13 of 'Gpd'
## 2.15 -> 2.17 (21/09/2011)
* (20/09/11) new version of `makedocrel.g` for building the manual
added file `gpd/examples/readall.g` for testing purposes
* (17/09/11) Shortened the banner.
* (16/09/11) Renamed subdirectory `xmod/gap` as `xmod/lib`
## 2.14 -> 2.15 (06/09/2011)
* (04/09/11) Changed BIND_GLOBAL to BindGlobal, since it is safer
* (16/08/11) changed directory for archive to `.../chda/gap4r5/xmod/`
## 2.13 -> 2.14 (30/07/2011)
* (30/07/11) final adjustments to the test files
* (29/07/11) major changes to `gp3objmap.g{d,i}`.
* (28/07/11) new 16/07/11 files now `dom2d3d.gd` etc.
* (27/07/11) ViewObj, PrintObj, Display, Name now methods for 2d-groups.
* (19/07/11) IsUp2dMapping now a category.
InducedXMod( s4, s3b, s3b ) fails due to iso to pc-group,
fo forced (for now) an isomorphism to a perm group.
* (18/07/11) Centre of an xmod no longer works, so brought back XModCentre.
* (16/07/11) Introduced a range of new categories in files
`dom2d.gd`, `dom2d.gi`, `map2d.gd`, `map2d.gi`.
As a result there were many changes in all files.
* (08/07/11) Changed headers of all files.
* (06/07/10) Changed XModByGroupOfAutomorphisms(G) in case G is pcgroup
* (02/07/10) New email address for Murat
* (30/06/10) Added check for IsPc2dDomain to PreXModObj
* (30/06/10) InducedXModByCopower now constructs a PcXMod if appropriate
* (28/06/10) Added methods for IsomorphismPcPreXMod, IsomorphismPcPreCat1
* (12/03/10) Moved 'XMod' development to IMac at home, and started v.2.14
## 2.12 -> 2.13 (21/01/2010)
* (21/01/10) Changed output of AllInducedXMods to list of StructureDesc.
## 2.11 -> 2.12 (24/11/2008)
* (19/11/08) GapDoc relegated to "suggested other packages".
## 2.008 -> 2.11 (13/11/2008)
* (13/11/08) added GNU General Public License declaration,
moved some 'XMod' utilities to `gpd/gap/util.g{d,i}`,
* (07/11/08) Changed website to: <www.maths.bangor.ac.uk/chda/xmod/>
Split the test file into one file per chapter.
* (30/04/08) Added GroupHomomorphismByImagesTriv to `util.gd`, `util.gi`
to allow both <gens> and <imgs> to be empty: triv -> triv!
Fixed bug in XModOfCat1 in assigning names.
FixedBug in Boundary for a pre-cat1-group.
* (31/03/08) Added function GpdBuildManualHTML()
* (16/03/08) renamed Tail,Head as TailMap,HeadMap (for benefit of 'Gpd')
* (08/10/07) started this CHANGES file;
changed directory permissions from 711 to 755;
renamed files: `obj2` -> `gp2obj`, etc, ready for groupoids;
added file `testall.g` in `xmod/tst`
## 2.007 -> 2.008 (25/10/2006)
* Fixed broken links in `PackageInfo.g`.
## 2.006 -> 2.007 (20/10/2006)
* Added basic functions for crossed squares, considered as 3dObjects
with crossed pairings, and their morphisms.
(Groups with two normal subgroups, and the actor of a crossed module,
provide standard examples. Cat2-groups are not yet implemented.)
* Converted the documentation to the format of the GAPDoc package,
and added the function XModBuildManual() to the `util.gi` file.
* Improved AutomorphismPermGroup for crossed modules, and introduced
a special method for conjugation crossed modules.
* Substantial revisons made to XModByCentralExtension, NorrieXMod,
LueXMod, ActorXMod, and InclusionInducedXModByCopower.
* Reintroduced the Cat1Select operation.
## 2.005 -> 2.006 (04/09/2004)
* Changed morphism functions to return fail when invalid data is supplied,
rather than calling Error.
* Fixed a bug in XModByGroupOfAutomorphisms.
## 2.004 -> 2.005 (16/04/2004)
* Moved the example files from `tst/test_i.g` to `examples/example_i.g`,
* converted `testmanual.g` to a proper test file `tst/xmod_manual.tst`.
* Replaced OperationHomomorphism by ActionHomomorphism,
a general GAP;4.4 change.
* Finished replacing RModule by AbelianModule.
* Renamed UpMapping as Up2dMapping.
* Added MappingGeneratorsImages and InverseGeneralMapping
for a 2dMapping.
* A significant change was the conversion of the actor crossed module
functions from the 3.4.4 version, including AutomorphismPermGroup
for a crossed module, WhiteheadXMod, NorrieXMod, LueXMod, ActorXMod,
Centre of a crossed module, InnerMorphism and InnerActorXMod.
* Added SmallerDegreePermPreXMod after discovering, in the library,
the very useful SmallerDegreePermutationRepresentation.
## 2.002 -> 2.004 (14/04/2004)
* gave a new email address for Murat Alp
* added the Cat1Select functionality of version 1 to the Cat1 function
## 2.001 -> 2.002 (January 2004)
* Version 2.002 was prepared for the 4.4 release at the end of January 2004,
and so required a `PackageInfo.g` file.
# Induced Crossed Modules (May 2002)
Converted combinatorial functions -- DistinctRepresentatives,
CommonRepresentatives, CommonTransversal and IsCommonTransversal.
Converted Tietze modification functions
TzCommutatorPair, TzPartition and FactorsPresentation.
Introduced global functions
IsomorphismPermObject, IsomorphismFpObject, and IsomorphismPcObject
which call IsomorphismPermGroup etc. when the object is a group.
Added functions IsomorphismPermPreXMod, IsomorphismPermPreCat1,
etc. to be called when the object is a 2d-object.
Added IsomorphismXModByNormalSubgroup which applies when the boundary
of the xmod is injective.
Added PreXModIsomorphismByIsomorphisms (but renamed 21/07/17)
(we also need a similar function PreCat1IsomorphismByIsomorphisms)
where the data consists of a crossed module, an isomorphism of the source,
and an isomorphism of the range.
Changed RModule to AbelianModule.
# Version 2.001 for GAP 4 (April 2002)
Generic name UpMapping chosen for derivations and sections
(later changed to Up2dMapping).
File names changed to `obj2.gd`, `map2.gi`, `up2.tex`, etc.
Added alternative methods for IsomorphismPermGroup for 2dObjects.
Sorted a problem with fixing the generating set for R when used to
define derivations. The (old) code used an fp-group version of R
and checks that all the relators map by chi to 1.
Unfortunately, IsomorphismFpGroup sometimes permutes the order
of the R-generators, with unfortunate effects.
The fix used IsomorphismFpGroupByGenerators, which returns the
images of the generators specified in the function call.
We have also used
genR := StrongGeneratorsStabChain( StabChain( rng ) );
throughout to specify the generators of R.
Operation XModMorphism renamed as XModMorphismByHoms, and a new
global function XModMorphism introduced (ditto for other 2dMappings).
Now using \chi_1 \star \chi_2 for Whitehead multiplication (on the right),
with CompositeDerivation still giving multiplication on the left.
This means that the second axiom for derivations and for sections has changed
-- see Chapter 4.
