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  4 Changes between GAP 4.7 and GAP 4.8
  
  This  chapter  contains an overview of the most important changes introduced
  in GAP 4.8.2 release (the 1st public release of GAP 4.8). Later it will also
  contain  information  about subsequent update releases for GAP 4.8. First of
  all,   the   GAP   development   repository  is  now  hosted  on  GitHub  at
  https://github.com/gap-system/gap,  and  GAP  4.8  is  the  first  major GAP
  release made from this repository. The public issue tracker for the core GAP
  system  is  located at https://github.com/gap-system/gap/issues, and you may
  use appropriate milestones from https://github.com/gap-system/gap/milestones
  to  see  all  changes that were introduced in corresponding GAP releases. An
  overview of the most significant ones is provided below.
  
  
  4.1 GAP 4.8.2 (February 2016)
  
  
  4.1-1 Changes in the core GAP system introduced in GAP 4.8
  
  New features:
  
      Added  support  for  profiling  which tracks how much time in spent on
        each line of GAP code. This can be used to show where code is spending
        a  long time and also check which lines of code are even executed. See
        the documentation for ProfileLineByLine (Reference: ProfileLineByLine)
        and  CoverageLineByLine (Reference: CoverageLineByLine) for details on
        generating  profiles, and the Profiling package for transforming these
        profiles into a human-readable form.
  
      Added  ability  to  install  (in  the library or packages) methods for
        accessing  lists  using multiple indices and indexing into lists using
        indices  other than positive small integers. Such methods could allow,
        for example, to support expressions like
  
          Example  
          m[1,2];
          m[1,2,3] := x;
          IsBound(m["a","b",Z(7)]);
          Unbind(m[1][2,3])
        
  
      Added  support  for  partially  variadic  functions  to allow function
        expressions like
  
          Example  
          function( a, b, c, x... ) ... end;
        
  
        which  would  require  at  least  three arguments and assign the first
        three  to  a, b and c and then a list containing any remaining ones to
        x.
  
        The  former special meaning of the argument arg is still supported and
        is now equivalent to function( arg... ), so no changes in the existing
        code are required.
  
      Introduced  CallWithTimeout and CallWithTimeoutList to call a function
        with  a  limit  on the CPU time it can consume. This functionality may
        not   be   available   on   all   systems   and   you   should   check
        GAPInfo.TimeoutsSupported  before  using  this  functionality.  (These
        functions were withdrawn in GAP 4.9.)
  
      GAP  now  displays  the  filename  and  line  numbers of statements in
        backtraces when entering the break loop.
  
      Introduced  TestDirectory  (Reference: TestDirectory) function to find
        (recursively)  all  .tst  files  from  a  given directory or a list of
        directories and run them using Test (Reference: Test).
  
  Improved and extended functionality:
  
      Method tracing shows the filename and line of function during tracing.
  
      TraceAllMethods  (Reference:  TraceAllMethods)  and  UntraceAllMethods
        (Reference:  UntraceAllMethods) to turn on and off tracing all methods
        in   GAP.  Also,  for  the  uniform  approach  UntraceImmediateMethods
        (Reference:  UntraceImmediateMethods)  has been added as an equivalent
        of TraceImmediateMethods(false).
  
      The  most  common cases of AddDictionary (Reference: AddDictionary) on
        three  arguments  now  bypass  method  selection, avoiding the cost of
        determining homogeneity for plain lists of mutable objects.
  
      Improved methods for symmetric and alternating groups in the "natural"
        representations and removed some duplicated code.
  
      Package  authors  may  optionally  specify the source code repository,
        issue  tracker  and  support email address for their package using new
        components  in  the  PackageInfo.g  file, which will be used to create
        hyperlinks  from the package overview page (see PackageInfo.g from the
        Example package which you may use as a template).
  
  Changed functionality:
  
      As   a   preparation   for   the   future   developments   to  support
        multithreading, some language extensions from the HPC-GAP project were
        backported  to  the  GAP library to help to unify the codebase of both
        GAP 4  and  HPC-GAP. The only change which is not backwards compatible
        is  that atomic, readonly and readwrite are now keywords, and thus are
        no longer valid identifiers. So if you have any variables or functions
        using that name, you will have to change it in GAP 4.8.
  
      There  was inconsistent use of the following properties of semigroups:
        IsGroupAsSemigroup, IsMonoidAsSemigroup, and IsSemilatticeAsSemigroup.
        IsGroupAsSemigroup was true for semigroups that mathematically defined
        a  group,  and  for  semigroups  in  the  category IsGroup (Reference:
        IsGroup);  IsMonoidAsSemigroup  was  only  true  for  semigroups  that
        mathematically  defined  monoids,  but  did not belong to the category
        IsMonoid   (Reference:  IsMonoid);  and  IsSemilatticeAsSemigroup  was
        simply   a   property   of   semigroups,   as  there  is  no  category
        IsSemilattice.
  
        From  version  4.8  onwards,  IsSemilatticeAsSemigroup  is  renamed to
        IsSemilattice,  and IsMonoidAsSemigroup returns true for semigroups in
        the category IsMonoid (Reference: IsMonoid).
  
        This  way  all  of  the  properties  of  the  type  IsXAsSemigroup are
        consistent.  It  should  be  noted that the only methods installed for
        IsMonoidAsSemigroup belong to the Semigroups and Smallsemi packages.
  
      ReadTest  became  obsolete and for backwards compatibility is replaced
        by  Test (Reference: Test) with the option to compare the output up to
        whitespaces.
  
      The  function  `ErrorMayQuit`,  which  differs  from Error (Reference:
        Error)  by  not  allowing  execution  to continue, has been renamed to
        ErrorNoReturn (Reference: ErrorNoReturn).
  
  Fixed bugs:
  
      A combination of two bugs could lead to a segfault. First off, NullMat
        (Reference:  NullMat) (and various other GAP functions), when asked to
        produce   matrix   over   a  small  field,  called  ConvertToMatrixRep
        (Reference:  ConvertToMatrixRep for a list (and a field)). After this,
        if  the  user  tried  to  change  one of the entries to a value from a
        larger  extension  field,  this  resulted  in  an  error. (This is now
        fixed).
  
        Unfortunately,  the  C  code catching this error had a bug and allowed
        users  to type return to continue while ignoring the conversion error.
        This  was  a bad idea, as the C code would be in an inconsistent state
        at this point, subsequently leading to a crash.
  
        This,  too,  has  been  fixed,  by not allowing the user to ignore the
        error by entering return.
  
      The   Fitting-free   code  and  code  inheriting  PCGS  is  now  using
        IndicesEANormalSteps   (Reference:  IndicesEANormalSteps)  instead  of
        IndicesNormalSteps  (Reference:  IndicesNormalSteps), as these indices
        are  neither  guaranteed,  nor  required  to be maximally refined when
        restricting to subgroups.
  
      A bug that caused a break loop in the computation of the Hall subgroup
        for groups having a trivial Fitting subgroup.
  
      Including  a break or continue statement in a function body but not in
        a loop now gives a syntax error instead of failing at run time.
  
      GroupGeneralMappingByImages  (Reference:  GroupGeneralMappingByImages)
        now verifies that that image of a mapping is contained in its range.
  
      Fixed a bug in caching the degree of transformation that could lead to
        a  non-identity  transformation accidentally changing its value to the
        identity transformation.
  
      Fixed  the problem with using Windows default browser as a help viewer
        using SetHelpViewer("browser");.
  
  
  4.1-2 New and updated packages since GAP 4.7.8
  
  At   the  time  of  the  release  of  GAP  4.7.8  there  were  119  packages
  redistributed   with   GAP.  New  packages  that  have  been  added  to  the
  redistribution since the release of GAP 4.7.8 are:
  
      CAP   (Categories,   Algorithms,  Programming)  package  by  Sebastian
        Gutsche,  Sebastian  Posur  and Øystein Skartsæterhagen, together with
        three       associated       packages      GeneralizedMorphismsForCAP,
        LinearAlgebraForCAP  and  ModulePresentationsForCAP  (all  three  - by
        Sebastian Gutsche and Sebastian Posur).
  
      Digraphs  package  by  Jan  De  Beule, Julius Jonušas, James Mitchell,
        Michael  Torpey  and Wilf Wilson, which provides functionality to work
        with graphs, digraphs, and multidigraphs.
  
      FinInG  package  by  John Bamberg, Anton Betten, Philippe Cara, Jan De
        Beule,  Michel  Lavrauw  and  Max Neunhöffer for computation in Finite
        Incidence Geometry.
  
      HeLP  package  by  Andreas  Bächle  and  Leo  Margolis, which computes
        constraints  on  partial  augmentations  of  torsion units in integral
        group  rings  using  a method developed by Luthar, Passi and Hertweck.
        The  package  can  be employed to verify the Zassenhaus Conjecture and
        the  Prime Graph Question for finite groups, once their characters are
        known.  It  uses  an  interface  to the software package 4ti2 to solve
        integral linear inequalities.
  
      matgrp package by Alexander Hulpke, which provides an interface to the
        solvable   radical   functionality  for  matrix  groups,  building  on
        constructive recognition.
  
      NormalizInterface  package by Sebastian Gutsche, Max Horn and Christof
        Söger,  which  provides  a  GAP interface to Normaliz, enabling direct
        access to the complete functionality of Normaliz, such as computations
        in  affine  monoids,  vector  configurations,  lattice  polytopes, and
        rational cones.
  
      profiling  package  by Christopher Jefferson for transforming profiles
        produced   by  ProfileLineByLine  (Reference:  ProfileLineByLine)  and
        CoverageLineByLine     (Reference:    CoverageLineByLine)    into    a
        human-readable form.
  
      Utils  package  by  Sebastian  Gutsche,  Stefan  Kohl  and Christopher
        Wensley, which provides a collection of utility functions gleaned from
        many packages.
  
      XModAlg  package by Zekeriya Arvasi and Alper Odabas, which provides a
        collection  of  functions  for  computing  with  crossed  modules  and
        Cat1-algebras and morphisms of these structures.
  
  
  4.2 GAP 4.8.3 (March 2016)
  
  
  4.2-1 Changes in the core GAP system introduced in GAP 4.8.3
  
  New features:
  
      New  function  TestPackage  (Reference:  TestPackage)  to run standard
        tests  (if  available) for a single package in the current GAP session
        (also  callable  via  make  testpackage PKGNAME=pkgname to run package
        tests in the same settings that are used for testing GAP releases).
  
  Improved and extended functionality:
  
      TestDirectory  (Reference:  TestDirectory) now prints a special status
        message  to  indicate  the outcome of the test (this is convenient for
        automated  testing).  If  necessary, this message may be suppressed by
        using the option suppressStatusMessage
  
      Improved output of tracing methods (which may be invoked, for example,
        with   TraceAllMethods  (Reference:  TraceAllMethods))  by  displaying
        filename and line number in some more cases.
  
  Changed functionality:
  
      Fixed  some  inconsistencies  in  the usage of IsGeneratorsOfSemigroup
        (Reference: IsGeneratorsOfSemigroup).
  
  Fixed bugs that could lead to incorrect results:
  
      Fallback  methods  for conjugacy classes, that were never intended for
        infinite  groups,  now  use  IsFinite  (Reference: IsFinite) filter to
        prevent  them  being  called  for  infinite groups. [Reported by Gabor
        Horvath]
  
  Fixed bugs that could lead to break loops:
  
      Calculating  stabiliser  for the alternating group caused a break loop
        in the case when it defers to the corresponding symmetric group.
  
      It   was  not  possible  to  use  DotFileLatticeSubgroups  (Reference:
        DotFileLatticeSubgroups)  for  a  trivial  group.  [Reported by Sergio
        Siccha]
  
      A   break   loop   while   computing   AutomorphismGroup   (Reference:
        AutomorphismGroup)  for  TransitiveGroup(12,269).  [Reported  by Ignat
        Soroko]
  
      A  break loop while computing conjugacy classes of PSL(6,4). [Reported
        by Martin Macaj]
  
  Other fixed bugs:
  
      Fix  for  using  Firefox  as  a default help viewer with SetHelpViewer
        (Reference: SetHelpViewer). [Reported by Tom McDonough]
  
  
  4.3 GAP 4.8.4 (June 2016)
  
  
  4.3-1 Changes in the core GAP system introduced in GAP 4.8.4
  
  New features:
  
      The GAP distribution now includes bin/BuildPackages.sh, a script which
        can  be started from the pkg directory via ../bin/BuildPackages.sh and
        will  attempt  to  build as many packages as possible. It replaces the
        InstPackages.sh  script  which  was not a part of the GAP distribution
        and  had  to  be  downloaded  separately from the GAP website. The new
        script  is  more  robust  and  simplifies  adding  new  packages  with
        binaries,  as  it  requires no adjustments if the new package supports
        the standard ./configure; make build procedure.
  
  Improved and extended functionality:
  
      SimpleGroup  (Reference:  SimpleGroup)  now  produces more informative
        error message in the case when AtlasGroup (AtlasRep: AtlasGroup) could
        not load the requested group.
  
      An   info  message  with  the  suggestion  to  use  InfoPackageLoading
        (Reference: InfoPackageLoading) will now be displayed when LoadPackage
        (Reference:  LoadPackage)  returns fail (unless GAP is started with -b
        option).
  
      The  build system will now enable C++ support in GMP only if a working
        C++ compiler is detected.
  
      More  checks  were  added when embedding coefficient rings or rational
        numbers into polynomial rings in order to forbid adding polynomials in
        different characteristic.
  
  Fixed bugs that could lead to crashes:
  
      Fixed  the  crash  in  --cover  mode when reading files with more than
        65,536 lines.
  
  Fixed bugs that could lead to incorrect results:
  
      Fixed  an  error in the code for partial permutations that occurred on
        big-endian systems. [Reported by Bill Allombert]
  
      Fixed  the  kernel  method  for  Remove  (Reference:  Remove) with one
        argument,  which failed to reduce the length of a list to the position
        of the last bound entry. [Reported by Peter Schauenburg]
  
  Fixed bugs that could lead to break loops:
  
      Fixed   the   break   loop   while   using  Factorization  (Reference:
        factorization)  on  permutation  groups by removing some old code that
        relied  on  further  caching  in  Factorization.  [Reported by Grahame
        Erskine]
  
      Fixed  a  problem  with  computation of maximal subgroups in an almost
        simple group. [Reported by Ramon Esteban Romero]
  
      Added  missing  methods  for  Intersection2 (Reference: Intersection2)
        when one of the arguments is an empty list. [Reported by Wilf Wilson]
  
  Other fixed bugs:
  
      Fixed    several   bugs   in   RandomPrimitivePolynomial   (Reference:
        RandomPrimitivePolynomial). [Reported by Nusa Zidaric]
  
      Fixed  several  problems with Random (Reference: Random) on long lists
        in 64-bit GAP installations.
  
  
  4.4 GAP 4.8.5 (September 2016)
  
  
  4.4-1 Changes in the core GAP system introduced in GAP 4.8.5
  
  Improved and extended functionality:
  
      The  error  messages produced when an unexpected fail is returned were
        made  more  clear  by explicitly telling that the result should not be
        boolean or fail (before it only said not a boolean).
  
      For      consistency,      both      NrTransitiveGroups     (transgrp:
        NrTransitiveGroups)  and  TransitiveGroup  (transgrp: TransitiveGroup)
        now disallow the transitive group of degree 1.
  
  Fixed bugs that could lead to incorrect results:
  
      A bug in the code for algebraic field extensions over non-prime fields
        that  may  cause, for example, a list of all elements of the extension
        not being a duplicate-free. [Reported by Huta Gana]
  
      So far, FileString (GAPDoc: FileString) only wrote files of sizes less
        than  2G  and did not indicate an error in case of larger strings. Now
        strings of any length can be written, and in the case of a failure the
        corresponding system error is shown.
  
  Fixed bugs that could lead to break loops:
  
      NaturalHomomorphismByIdeal (Reference: NaturalHomomorphismByIdeal) was
        not reducing monomials before forming a quotient ring, causing a break
        loop on some inputs. [Reported by Dmytro Savchuk]
  
      A  bug  in DefaultInfoHandler (Reference: DefaultInfoHandler) caused a
        break   loop   on   startup   with   the   setting  SetUserPreference(
        "InfoPackageLoadingLevel", 4 )`. [Reported by Mathieu Dutour]
  
      The  Iterator  (Reference: Iterator) for permutation groups was broken
        when the StabChainMutable (Reference: StabChainMutable for a group) of
        the  group  was not reduced, which can reasonably happen as the result
        of various algorithms.
  
  
  4.5 GAP 4.8.6 (November 2016)
  
  
  4.5-1 Changes in the core GAP system introduced in GAP 4.8.6
  
  Fixed bugs that could lead to break loops:
  
      Fixed  regression  in  the GAP kernel code introduced in GAP 4.8.5 and
        breaking   StringFile   (GAPDoc:  StringFile)  ability  to  work  with
        compressed files. [Reported by Bill Allombert]
  
  
  4.6 GAP 4.8.7 (March 2017)
  
  
  4.6-1 Changes in the core GAP system introduced in GAP 4.8.7
  
  Fixed bugs that could lead to incorrect results:
  
      Fixed  a regression from GAP 4.7.6 when reading compressed files after
        a  workspace  is loaded. Before the fix, if GAP is started with the -L
        option  (load  workspace), using ReadLine (Reference: ReadLine) on the
        input   stream   for  a  compressed  file  returned  by  InputTextFile
        (Reference:   InputTextFile)   only   returned  the  first  character.
        [Reported by Bill Allombert]
  
  Other fixed bugs:
  
      Fixed  compiler warning occurring when GAP is compiled with gcc 6.2.0.
        [Reported by Bill Allombert]
  
  
  4.6-2 New and updated packages since GAP 4.8.6
  
  This  release  contains  updated  versions  of  19  packages  from GAP 4.8.6
  distribution.  Additionally,  the  following  package has been added for the
  redistribution with GAP:
  
      lpres package (author: René Hartung, maintainer: Laurent Bartholdi) to
        work  with  L-presented  groups,  namely  groups  given  by  a  finite
        generating  set  and  a  possibly  infinite  set of relations given as
        iterates   of  finitely  many  seed  relations  by  a  finite  set  of
        endomorphisms. The package implements nilpotent quotient, Todd-Coxeter
        and Reidemeister-Schreier algorithms for such groups.
  
  
  4.7 GAP 4.8.8 (August 2017)
  
  
  4.7-1 Changes in the core GAP system introduced in GAP 4.8.8
  
  Fixed bugs that could lead to incorrect results:
  
      Fixed  a bug in RepresentativeAction (Reference: RepresentativeAction)
        producing incorrect answers for both symmetric and alternating groups,
        with  both  OnTuples  (Reference:  OnTuples)  and  OnSets  (Reference:
        OnSets), by producing elements outside the group. [Reported by Mun See
        Chang]
  
  Fixed bugs that could lead to break loops:
  
      Fixed  a bug in RepresentativeAction (Reference: RepresentativeAction)
        for S_n and A_n acting on non-standard domains.
  
  Other fixed bugs:
  
      Fixed  a  problem  with  checking  the  path  to a file when using the
        default  browser  as  a  help  viewer  on  Windows.  [Reported by Jack
        Saunders]
  
  
  4.7-2 New and updated packages since GAP 4.8.7
  
  This  release  contains  updated  versions  of  29  packages  from GAP 4.8.7
  distribution. Additionally, the Gpd package (author: Chris Wensley) has been
  renamed to Groupoids.