GAP (changes) - Chapter 3: Changes between GAP 4.8 and GAP 4.9

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3 Changes between GAP 4.8 and GAP 4.9
3.1 GAP 4.9.1 (May 2018)
3.1-1 Changes in the core GAP system introduced in GAP 4.9
3.1-2 HPC-GAP
3.1-3 New and updated packages since GAP 4.8.10
3.2 GAP 4.9.2 (July 2018)
3.2-1 Changes in the core GAP system introduced in GAP 4.9.2
3.2-2 New and updated packages since GAP 4.9.1
3.3 GAP 4.9.3 (September 2018)
3.3-1 Changes in the core GAP system introduced in GAP 4.9.3
3.3-2 New and updated packages since GAP 4.9.2

### 3 Changes between GAP 4.8 and GAP 4.9

This chapter contains an overview of the most important changes introduced in GAP 4.9.1 release (the 1st public release of GAP 4.9). Later it will also contain information about subsequent update releases for GAP 4.9.

These changes are also listed on the Wiki page https://github.com/gap-system/GAP/wiki/gap-4.9-release-notes.

#### 3.1 GAP 4.9.1 (May 2018)

##### 3.1-1 Changes in the core GAP system introduced in GAP 4.9

Major changes:

- Merged HPC-GAP into GAP. For details, please refer to Subsection 3.1-2 at the end of these release notes.

- GAP has a new build system, which resolves many quirks and issues with the old system, and will be easier to maintain. For regular users, the usual `./configure && make` should work fine as before. If you are interested in technical details on the new build system, take a look at `README.buildsys.md`.

- The guidelines for developing GAP packages were revised and moved from the Example package to Reference: Using and Developing GAP Packages (#484).

- In addition to supporting single argument lambda functions like `a -> a+1`, GAP now supports lambdas with fewer or more than one argument, or even a variable number. E.g. `{a,b} -> a+b` is a shorthand for `function(a,b) return a+b; end`. For details on how to use this, see Reference: Function. For technical details, e.g. why we did not choose the syntax `(a,b) -> a+b`, see #490.

- Function calls, list accesses and records accesses now can be nested. For example, you can now write `y := f().x;` (essentially equivalent to `y := f();; y := y.x;`), which previously would have resulted in an error; see #457 and #462).

- The libraries of small, primitive and transitive groups which previously were an integral part of GAP were split into three separate packages PrimgGrp, SmallGrp and TransGrp. For backwards compatibility, these are required packages in GAP 4.9 (i.e., GAP will not start without them). We plan to change this for GAP 4.10 (see #2434), once all packages which currently implicitly rely on these new packages had time to add explicit dependencies on them (#1650, #1714).

- The performance of GAP's sorting functions (such as `Sort` (Reference: Sort), `SortParallel` (Reference: SortParallel), etc.) has been substantially improved, in some examples by more than a factor of four: as a trivial example, compare the timing for `Sort([1..100000000] * 0)`. As a side effect, the result of sorting lists with equal entries may produce different answers compared to previous GAP versions. If you would like to make your code independant of the exact employed sorting algorithm, you can use the newly added `StableSort` (Reference: StableSort), `StableSortBy` (Reference: StableSortBy) and `StableSortParallel` (Reference: StableSortParallel). (For some technical details, see #609).

- We removed our old home-grown big integer code, and instead always use the GMP based big integer code. This means that the GMP library now is a required dependency, not just an optional one. Note that GAP has been using GMP big integer arithmetic for a long time by default, and we also have been bundling GMP with GAP. So this change mostly removed code that was never in use for most users.

- A number of improvements have been made to `Random` (Reference: Random). These may lead to different sequences of numbers being created. On the up side, many more methods for `Random` (Reference: Random) (and other `RandomXYZ` operations) now optionally take an explicit `RandomSource` (Reference: RandomSource) as first argument (but not yet all: help with issue #1098 is welcome). Some relevant pull requests:

  - Allow creating random permutations using a random source (#1165)

  - Let more `Random` (Reference: Random) methods use an alternative source (#1168)

  - Help `Random` (Reference: Random) methods to use `RandomSource` (Reference: RandomSource) (#810)

  - Remove uses of old random generator (#808)

  - Fix `Random` (Reference: Random) on long (>2^28) lists (#781)

  - Fix `RandomUnimodularMat` (Reference: RandomUnimodularMat) (#1511)

  - Use `RandomSource` (Reference: RandomSource) in a few more places (#1599)

- The output and behaviour of the profiling system has been substantially improved:

  - Make profiling correctly handle the same file being opened multiple times (#1069)

  - Do not profile the `return` statements (Reference: return) inserted into the end of functions (#1073)

  - Ensure we reset `OutputtedFilenameList` in profiling when a workspace is restored (#1164)

  - Better tracking of amounts of memory allocated and time spent in the garbage collector (#1806)

  - Allow profiling of memory usage (#1808)

  - Remove profiling limit on files with <= 2^16 lines (#1913)

- In many cases GAP now outputs the filename and location of functions in helpful places, e.g. in error messages or when displaying compiled functions. We also try to always use the format `FILENAME:LINE`, which various utilities already know how to parse (e.g. in iTerm2, cmd-clicking on such a string can be configured to open an editor for the file at the indicated line). For some technical details, see #469, #755, #1058.

- GAP now supports constant variables, whose value cannot change anymore during runtime; code using such constants can then be slightly optimized by GAP. E.g. if `foo` is turned into a constant variable bound to the value `false`, then GAP can optimize `if foo then ... fi;` blocks completely away. For details, see `MakeConstantGlobal` (Reference: MakeConstantGlobal) in Reference: More About Global Variables. (#1682, #1770)

Other changes:

- Enhance `StructureDescription` (Reference: StructureDescription) with a major rewrite, enhancing `DirectFactorsOfGroup"` and adding `SemidirectDecompositions`; the core algorithm now also works for infinite abelian groups. Further, it became faster by quickly finding abelian direct factors and recognizing several cases where the group is direct indecomposable. (#379, #763, #985)

- Mark `FittingSubgroup` (Reference: FittingSubgroup) and `FrattiniSubgroup` (Reference: FrattiniSubgroup) as nilpotent (#400)

- Add method for `Socle` (Reference: Socle) for finite nilpotent groups (#402)

- Change `ViewString` (Reference: ViewString) and `String` (Reference: String) methods for various inverse semigroups and monoids (#438, #880, #882)

- Enhance some nilpotent and p-group attributes (#442)

- Improve `Union` (Reference: Union) for a list with many ranges (#444)

- Add `UserHomeExpand` (Reference: UserHomeExpand), a function to expand `~` in filenames. (#447)

- Extra hint in "No Method Found" error message if one of the arguments is `fail` (#460)

- Tell Sylow subgroups of natural A_n or S_n their size when we make them (#529)

- Some small enhancements on Sylow and Hall subgroup computations, mostly for nilpotent groups. (#535)

- Remove `.zoo` archive related tools (#540)

- Add new `FrattiniSubgroup` (Reference: FrattiniSubgroup), `MaximalNormalSubgroups` (Reference: MaximalNormalSubgroups), `MinimalNormalSubgroups` (Reference: MinimalNormalSubgroups) and `Socle` (Reference: Socle) methods for abelian and/or solvable groups, even infinite ones. The new methods are only triggered if the group already knows that it is abelian and/or solvable. (#552, #583, #606)

- New attribute `NormalHallSubgroups`, returning a list of all normal Hall subgroups of a group. (#561)

- Add `ComplementClassesRepresentatives` (Reference: ComplementClassesRepresentatives) fallback method for arbitrary groups (#563)

- (#612) Add parsing of hex literals in strings, e.g. `"\0x61"` is turned into `"a"` (#612)

- Collection of enhancements (#683)

- Various speed improvements to polynomial factorisation and the GAP MeatAxe (#720, #1027)

- The code and documentation for transformations is improved and corrected in many instances (#727, #732)

- Change `RootFFE` to optionally takes a field or field size as first argument, from which the roots will be taken (#761)

- Change `Permanent` (Reference: Permanent) from a global function to an attribute (#777)

- Add `CallFuncListWrap` (Reference: CallFuncListWrap) to wrap return value to allow distinguishing between functions which return and functions which don't (#824)

- Allow repeated use of same `DeclareSynonym` (Reference: DeclareSynonym) call (#835)

- New implementation of modified Todd-Coxeter (the old one had bugs, see #302), #843)

- New functionality: Cannon/Holt automorphisms and others (#878)

- Add `IsPowerfulPGroup` (Reference: IsPowerfulPGroup) property, and a `FrattiniSubgroup` (Reference: FrattiniSubgroup) method for powerful p-groups (#894)

- Improve performance for group isomorphism/automorphisms (#896, #968)

- Make `ListX` (Reference: ListX), `SetX` (Reference: SetX), `SumX` (Reference: SumX) and `ProductX` (Reference: ProductX) support lists which are not collections (#903)

- Some improvements for `LatticeByCyclicExtension` (Reference: LatticeByCyclicExtension) (#905)

- Add helpers to retrieve information about operations and filters: `CategoryByName` (Reference: CategoryByName), `TypeOfOperation` (Reference: TypeOfOperation), `FilterByName` (Reference: FilterByName), `FiltersObj` (Reference: FiltersObj), `FiltersType` (Reference: FiltersType), `IdOfFilter`, `IdOfFilterByName`, `IsAttribute` (Reference: IsAttribute), `IsCategory` (Reference: IsCategory), `IsProperty` (Reference: IsProperty), `IsRepresentation` (Reference: IsRepresentation) (#925, #1593)

- Add case-insensitive autocomplete (#928)

- Give better error message if a help file is missing (#939)

- Add `LowercaseChar` (Reference: LowercaseChar) and `UppercaseChar` (Reference: UppercaseChar) (#952)

- Add `PositionMaximum` (Reference: PositionMaximum) and `PositionMinimum` (Reference: PositionMinimum) (#956)

- Switching default command history length from infinity to 1000 (#960)

- Allow conversion of `-infinity` to float via `NewFloat` (Reference: NewFloat) and `MakeFloat` (Reference: MakeFloat) (#961)

- Add option `NoPrecomputedData` to avoid use of data libraries in certain computations (useful if one wants to verify the content of these data libraries) (#986)

- Remove one-argument version of `AsPartialPerm` (Reference: AsPartialPerm for a permutation and a set of positive integers) for a transformation (#1036)

- Partial perms now have a `MultiplicativeZero` (Reference: MultiplicativeZero) rather than a `Zero` (Reference: Zero), since they are multiplicative rather than additive elements (#1040)

- Various enhancements: (#1046)

  - A bugfix in `NaturalHomomorphismByIdeal` (Reference: NaturalHomomorphismByIdeal) for polynomial rings

  - Improvements in handling solvable permutation groups

  - The trivial group now is a member of the perfect groups library

  - Improvements in using tabulated data for maximal subgroups

- New tests for group constructors and some fixes (e.g. `GO(1,4,5)` used to trigger an error) (#1053)

- Make `HasSolvableFactorGroup` slightly more efficient (#1062)

- Enhance `HasXXFactorGroup` (#1066)

- Remove GAP4stones from tests (#1072)

- `AsMonoid` (Reference: AsMonoid) and `AsSemigroup` (Reference: AsSemigroup) are now operations, and various bugs were resolved related to isomorphisms of semigroups and monoids (#1112)

- Mark isomorphisms between trivial groups as bijective (#1116)

- Speed up `RootMod` (Reference: RootMod) and `RootsMod` (Reference: RootsMod) for moduli with large prime factors; also add `IS_PROBAB_PRIME_INT` kernel function (#1141)

- The search for the documentation of system setters and testers now returns corresponding attributes and properties (#1144)

- Remove command line options `-c`, `-U`, `-i` and `-X`, add `--quitonbreak` (#1192, #1265, #1421, #1448)

- Remove Itanium support (#1163)

- Adding two strings now shows a more helpful error message (#1314)

- Suppress `Unbound global variable` warning in `IsBound` (Reference: IsBound for a global variable) (#1334)

- Increase warning level for Conway polynomial (#1363)

- Performance improvements to maximal and intermediate subgroups, fix of `RepresentativeAction` (Reference: RepresentativeAction) (#1390)

- Revise Chapter 52 of the reference manual (fp semigroups and monoids) (#1441)

- Improve the performance of the `Info` (Reference: Info) statement (#1464, #1770)

- When printing function bodies, avoid some redundant spaces (#1498)

- Add kernel functions for directly accessing entries of GF2/8bit compressed matrices (#1585)

- Add `String` (Reference: String) method for functions (#1591)

- Check modules were compiled with the same version of GAP when loading them (#1600)

- When printing function, reproduce `TryNextMethod()` correctly (#1613)

- New "Bitfields" feature (Reference: Bitfields) providing efficient support for packing multiple data items into a single word for cache and memory efficiency (#1616)

- Improved `bin/BuildPackages.sh`, in particular added option to abort upon failure (#2022)

- Rewrote integer code (GMP) for better performance of certain large integer operations, and added kernel implementations of various functions, including these:

  - Add kernel implementations of `AbsInt` (Reference: AbsInt), `SignInt` (Reference: SignInt); add new kernel functions `ABS_RAT`, `SIGN_RAT`; and speed up Reference: mod, `RemInt` (Reference: RemInt), `QuoInt` (Reference: QuoInt) for divisors which are small powers of 2 (#1045)

  - Add kernel implementations of `Jacobi` (Reference: Jacobi), `PowerModInt` (Reference: PowerModInt), `Valuation` (Reference: Valuation) (for integers), `PValuation` (Reference: PValuation) (for integers) (#1075)

  - Add kernel implementation of `Factorial` (Reference: Factorial) (#1969)

  - Add kernel implementation of `Binomial` (Reference: Binomial) (#1921)

  - Add kernel implementation of `LcmInt` (Reference: LcmInt) (#2019)

- Check version of kernel for package versions (#1600)

- Add new `AlgebraicExtensionNC` (Reference: AlgebraicExtensionNC) operation (#1665)

- Add `NumberColumns` and `NumberRows` to `MatrixObj` interface (#1657)

- `MinimalGeneratingSet` (Reference: MinimalGeneratingSet) returns an answer for non-cyclic groups that already have a generating set of size 2 (which hence is minimal) (#1755)

- Add `GetWithDefault` (Reference: GetWithDefault) which returns the n-th element of the list if it is bound, and the default value otherwise (#1762)

- Fast method for `ElmsBlist` when positions are a range with increment 1 (#1773)

- Make permutations remember their inverses (#1831)

- Add invariant forms for `GU(1,q)` and `SU(1,q)` (#1874)

- Implement `StandardAssociate` (Reference: StandardAssociate) and `StandardAssociateUnit` (Reference: StandardAssociateUnit) for `ZmodnZ` (Reference: ZmodnZ), clarify documentation for `IsEuclideanRing` (Reference: IsEuclideanRing) (#1990)

- Improve documentation and interface for floats (#2016)

- Add `PositionsProperty` (Reference: PositionsProperty) method for non-dense lists (#2021)

- Add `TrivialGroup(IsFpGroup)` (#2037)

- Change `ObjectifyWithAttributes` (Reference: ObjectifyWithAttributes) to return the new objects (#2098)

- Removed a never released undocumented HPC-GAP syntax extension which allowed to use a backtick/backquote as alias for `MakeImmutable` (Reference: MakeImmutable). (#2202).

- Various changes (#2253):

  - Improve performance and memory usage of `ImageKernelBlocksHomomorphism"`

  - Document `LowIndexSubgroups` (Reference: LowIndexSubgroups)

  - Correct `ClassesSolvableGroup` (Reference: ClassesSolvableGroup) documentation to clarify that it requires, but does not test membership

  - fix `IsNaturalGL` (Reference: IsNaturalGL) for trivial matrix groups with empty generating set

- Make it possible to interrupt `repeat continue; until false;` and similar tight loops with "Ctrl-C" (#2259).

- Improved GAP testing infrastructure, extended GAP test suite, and increased code coverage

- Countless other tweaks, improvements, fixes were applied to the GAP library, kernel and manual

Fixed bugs:

- Fix bugs in `NormalSubgroups` (Reference: NormalSubgroups) and `PrintCSV` (Reference: PrintCSV) (#433)

- Fix nice monomorphism dispatch for `HallSubgroup` (Reference: HallSubgroup) (e.g. fixes `HallSubgroup(GL(3,4), [2,3])`) (#559)

- Check for permutations whose degree would exceed the internal limit, and document that limit (#581)

- Fix segfault after quitting from the break loop in certain cases (#709 which fixes #397)

- Fix rankings for `Socle` (Reference: Socle) and `MinimalNormalSubgroups` (Reference: MinimalNormalSubgroups) (#711)

- Make key and attribute values immutable (#714)

- Make `OnTuples([-1], (1,2))` return an error (#718)

- Fix bug in `NewmanInfinityCriterion` (Reference: NewmanInfinityCriterion) which could corrupt the `PCentralSeries` (Reference: PCentralSeries) attribute (#719)

- The length of the list returned by `OnSetsPerm` is now properly set (#731)

- Fix `Remove` (Reference: Remove) misbehaving when last member of list with gaps in it is removed (#766)

- Fix bugs in various methods for Rees (0-)matrix semigroups: `IsFinite` (Reference: IsFinite), `IsOne` (Reference: IsOne), `Enumerator` (Reference: Enumerator), `IsReesMatrixSemigroup` (Reference: IsReesMatrixSemigroup) and `IsReesZeroMatrixSemigroup` (Reference: IsReesZeroMatrixSemigroup) (#768, #1676)

- Fix `IsFullTransformationSemigroup` (Reference: IsFullTransformationSemigroup) to work correctly for the full transformation semigroup of degree 0 (#769)

- Fix printing very large (> 2^28 points) permutations (#782)

- Fix `Intersection([])` (#854)

- Fix crash in `IsKernelFunction` for some inputs (#876)

- Fix bug in `ShortestVectors` (Reference: ShortestVectors) which could cause `OrthogonalEmbeddings` (Reference: OrthogonalEmbeddings) to enter a break loop (#941)

- Fix crash in some methods involving partial perms (#948)

- `FreeMonoid(0)` no longer satisfies `IsGroup` (Reference: IsGroup) (#950)

- Fix crash when invoking weak pointer functions on invalid arguments (#1009)

- Fix a bug parsing character constants (#1015)

- Fix several bugs and crashes in `Z(p,d)` for invalid arguments, e.g. `Z(4,5)`, `Z(6,3)` (#1029, #1059, #1383, #1573)

- Fix starting GAP on systems with large inodes (#1033)

- Fix `NrFixedPoints` (Reference: NrFixedPoints for a partial perm) and `FixedPointsOfPartialPerm` (Reference: FixedPointsOfPartialPerm for a partial perm) for a partial perm and a partial perm semigroup (they used to return the moved points rather than the fixed points) (#1034)

- Fix `MeetOfPartialPerms` (Reference: MeetOfPartialPerms) when given a collection of 1 or 0 partial perms (#1035)

- The behaviour of `AsPartialPerm` (Reference: AsPartialPerm for a transformation and a set of positive integer) for a transformation and a list is corrected (#1036)

- `IsomorphismReesZeroMatrixSemigroup` (Reference: IsomorphismReesZeroMatrixSemigroup) for a 0-simple semigroup is now defined on the zero of the source and range semigroups (#1038)

- Fix isomorphisms from finitely-presented monoids to finitely-presented semigroups, and allow isomorphisms from semigroups to fp-monoids (#1039)

- Fix `One` (Reference: One) for a partial permutation semigroup without generators (#1040)

- Fix `MemoryUsage` (Reference: MemoryUsage) for positional and component objects (#1044)

- Fix `PlainString` causing immutable strings to become mutable (#1096)

- Restore support for sparc64 (#1124)

- Fix a problem with `<` for transformations, which could give incorrect results (#1130)

- Fix crash when comparing recursive data structures such as `[~] = [~]` (#1151)

- Ensure output of `TrivialGroup(IsPermGroup)` has zero generators (#1247)

- Fix for applying the `InverseGeneralMapping` (Reference: InverseGeneralMapping) of an `IsomorphismFpSemigroup` (Reference: IsomorphismFpSemigroup) (#1259)

- Collection of improvements and fixes: (#1294)

  - A fix for quotient rings of rings by structure constants

  - Generic routine for transformation matrix to rational canonical form

  - Speed improvements to block homomorphisms

  - New routines for conjugates or subgroups with desired containment

  - Performance improvement for conjugacy classes in groups with a huge number of classes, giving significant improvements to `IntermediateSubgroups` (Reference: IntermediateSubgroups) (e.g. 7-Sylow subgroup in PSL(7,2)), ascending chain and thus in turn double coset calculations and further routines that rely on it

- Fix `EqFloat` (Reference: EqFloat) to return correct results, instead of always returning `false` (#1370)

- Various changes, including fixes for `CallFuncList` (Reference: CallFuncList) (#1417)

- Better define the result of `MappingPermListList` (Reference: MappingPermListList) (#1432)

- Check the arguments to `IsInjectiveListTrans` (Reference: IsInjectiveListTrans) to prevent crashes (#1435)

- Change `BlownUpMat` (Reference: BlownUpMat) to return fail for certain invalid inputs (#1488)

- Fixes for creating Green's classes of semigroups (#1492, #1771)

- Fix `DoImmutableMatrix` for finite fields (#1504)

- Make structural copy handle boolean lists properly (#1514)

- Minimal fix for algebraic extensions over finite fields of order > 256 (#1569)

- Fix for computing quotients of certain algebra modules (#1669)

- Fix an error in the default method for `PositionNot` (Reference: PositionNot) (#1672)

- Improvements to Rees matrix semigroups code and new tests (#1676)

- Fix `CodePcGroup` (Reference: CodePcGroup) for the trivial polycyclic group (#1679)

- Fix `FroidurePinExtendedAlg` for partial permutation monoids (#1697)

- Fix computing the radical of a zero dimensional associative algebra (#1701)

- Fix a bug in `RadicalOfAlgebra` (Reference: RadicalOfAlgebra) which could cause a break loop for some associative algebras (#1716)

- Fix a recursion depth trap error when repeatedly calling `Test` (Reference: Test) (#1753)

- Fix bugs in `PrimePGroup` (Reference: PrimePGroup) for direct products of p-groups (#1754)

- Fix `UpEnv` (Reference: UpEnv) (available in break loops) when at the bottom of the backtrace (#1780)

- Fix `IsomorphismPartialPermSemigroup` (Reference: IsomorphismPartialPermSemigroup) and `IsomorphismPartialPermMonoid` (Reference: IsomorphismPartialPermMonoid) for permutation groups with 0 generators (#1784)

- Fix `DisplaySemigroup` (Reference: DisplaySemigroup) for transformation semigroups (#1785)

- Fix "no method found" errors in `MagmaWithOne` (Reference: MagmaWithOne) and `MagmaWithInverses` (Reference: MagmaWithInverses) (#1798)

- Fix an error computing kernel of group homomorphism from fp group into permutation group (#1809)

- Fix an error in MTC losing components when copying a new augmented coset table (#1809)

- Fix output of `Where` (Reference: Where) in a break loop, which pointed at the wrong code line in some cases (#1814)

- Fix the interaction of signals in GAP and the IO package (#1851)

- Make line editing resilient to `LineEditKeyHandler` failure (in particular, don't crash) (#1856)

- Omit non-characters from `PermChars` (Reference: PermChars) results (#1867)

- Fix `ExteriorPower` (Reference: ExteriorPowerOfAlgebraModule) when exterior power is 0-dimensional (used to return a 1-dimensional result) (#1872)

- Fix recursion depth trap and other improvements for quotients of fp groups (#1884)

- Fix a bug in the computation of a permutation group isomorphic to a group of automorphisms (#1907)

- Fix bug in `InstallFlushableValueFromFunction` (Reference: InstallFlushableValueFromFunction) (#1920)

- Fix `ONanScottType` (Reference: ONanScottType) and introduce `RestrictedInverseGeneralMapping` (Reference: RestrictedInverseGeneralMapping) (#1937)

- Fix `QuotientMod` (Reference: QuotientMod) documentation, and the integer implementation. This partially reverts changes made in version 4.7.8 in 2013. The documentation is now correct (resp. consistent again), and several corner cases, e.g. `QuotientMod(0,0,m)` now work correctly (#1991)

- Fix `PositionProperty` (Reference: PositionProperty) with from < 1 (#2056)

- Fix inefficiency when dealing with certain algebra modules (#2058)

- Restrict capacity of plain lists to 2^28 in 32-bit and 2^60 in 64-bit builds (#2064)

- Fix crashes with very large heaps (> 2 GB) on 32 bit systems, and work around a bug in `memmove` in 32-bit glibc versions which could corrupt memory (affects most current Linux distributions) (#2166).

- Fix name of the `reversed` option in documentation of `LoadAllPackages` (Reference: LoadAllPackages) (#2167).

- Fix `TriangulizedMat([])` (see `TriangulizedMat` (Reference: TriangulizedMat) to return an empty list instead of producing an error (#2260).

- Fix several potential (albeit rare) crashes related to garbage collection (#2321, #2313, #2320).

Removed or obsolete functionality:

- Make `SetUserPreferences` obsolete (use `SetUserPreference` (Reference: SetUserPreference) instead) (#512)

- Remove undocumented `NameIsomorphismClass` (#597)

- Remove unused code for rational classes of permutation groups (#886)

- Remove unused and undocumented `Randomizer` and `CheapRandomizer` (#1113)

- Remove `install-tools.sh` script and documentation mentioning it (#1305)

- Withdraw `CallWithTimeout` and `CallWithTimeoutList` (#1324)

- Make `RecFields` obsolete (use `RecNames` (Reference: RecNames) instead) (#1331)

- Remove undocumented `SuPeRfail` and `READ_COMMAND` (#1374)

- Remove unused `oldmatint.gi` (old methods for functions that compute Hermite and Smith normal forms of integer matrices) (#1765)

- Make `TRANSDEGREES` obsolete (#1852)

##### 3.1-2 HPC-GAP

GAP includes experimental code to support multithreaded programming in GAP, dubbed HPC-GAP (where HPC stands for "high performance computing"). GAP and HPC-GAP codebases diverged during the project, and we are currently working on unifying the codebases and incorporating the HPC-GAP code back into the mainstream GAP versions.

This is work in progress, and HPC-GAP as it is included with GAP right now still suffers from various limitations and problems, which we are actively working on to resolve. However, including it with GAP (disabled by default) considerably simplifies development of HPC-GAP. It also means that you can very easily get a (rough!) sneak peak of HPC-GAP. It comes together with the new manual book called "HPC-GAP Reference Manual" and located in the `doc/hpc` directory.

Users interested in experimenting with shared memory parallel programming in GAP can build HPC-GAP by following the instructions from https://github.com/gap-system/gap/wiki/Building-HPC-GAP. While it is possible to build HPC-GAP from a release version of GAP you downloaded from the GAP website, due to the ongoing development of HPC-GAP, we recommend that you instead build HPC-GAP from the latest development version available in the GAP repository at GitHub, i.e. https://github.com/gap-system/gap.

##### 3.1-3 New and updated packages since GAP 4.8.10

There were 132 packages redistributed together with GAP 4.8.10. The GAP 4.9.1 distribution includes 134 packages, including numerous updates of previously redistributed packages, and some major changes outlined below.

The libraries of small, primitive and transitive groups which previously were an integral part of GAP were split into three separate packages PrimgGrp, SmallGrp and TransGrp:

- The PrimGrp package by Alexander Hulpke, Colva M. Roney-Dougal and Christopher Russell provides the library of primitive permutation groups which includes, up to permutation isomorphism (i.e., up to conjugacy in the corresponding symmetric group), all primitive permutation groups of degree < 4096.

- The SmallGrp package by Bettina Eick, Hans Ulrich Besche and Eamonn O’Brien provides the library of groups of certain "small" orders. The groups are sorted by their orders and they are listed up to isomorphism; that is, for each of the available orders a complete and irredundant list of isomorphism type representatives of groups is given.

- The TransGrp package by Alexander Hulpke provides the library of transitive groups, with an optional download of the library of transitive groups of degree 32.

For backwards compatibility, these are required packages in GAP 4.9 (i.e., GAP will not start without them). We plan to change this for GAP 4.10 (see #2434), once all packages which currently implicitly rely on these new packages had time to add explicit dependencies on them (#1650, #1714).

The new ZeroMQInterface package by Markus Pfeiffer and Reimer Behrends has been added for the redistribution. It provides both low-level bindings as well as some higher level interfaces for the ZeroMQ message passing library for GAP and HPC-GAP enabling lightweight distributed computation.

The HAPprime package by Paul Smith is no longer redistributed with GAP. Part of the code has been incorporated into the HAP package. Its source code repository, containing the code of the last distributed version, can still be found at https://github.com/gap-packages/happrime.

Also, the ParGAP package by Gene Cooperman is no longer redistributed with GAP because it no longer can be compiled with GAP 4.9 (see this announcement). Its source code repository, containing the code of the last distributed version, plus some first fixes needed for compatibility for GAP 4.9, can still be found at https://github.com/gap-packages/pargap. If somebody is interested in repairing this package and taking over its maintenance, so that it can be distributed again, please contact the GAP team.

#### 3.2 GAP 4.9.2 (July 2018)

##### 3.2-1 Changes in the core GAP system introduced in GAP 4.9.2

Fixed bugs that could lead to break loops:

- Fixed a bug in iterating over an empty cartesian product (#2421). [Reported by @isadofschi]

Fixed bugs that could lead to crashes:

- Fixed a crash after entering `return;` in a "method not found" break loop (#2449).

- Fixed a crash when an error occurs and `OutputLogTo` (Reference: OutputLogTo for streams) points to a stream which internally uses another stream (#2596).

Fixed bugs that could lead to incorrect results:

- Fixed a bug in computing maximal subgroups, which broke some other calculations, in particular, computing intermediate subgroups. (#2488). [Reported by Seyed Hassan Alavi]

Other fixed bugs and further improvements:

- Profiling now correctly handles calls to `longjmp` and allows to generate profiles using version 2.0.1 of the Profiling package (#2444).

- The `bin/gap.sh` script now respects the `GAP_DIR` environment variable (#2465). [Contributed by RussWoodroofe]

- The `bin/BuildPackages.sh` script now properly builds binaries for the simpcomp package (#2475).

- Fixed a bug in restoring a workspace, which prevented GAP from saving the history if a workspace was loaded during startup (#2578).

##### 3.2-2 New and updated packages since GAP 4.9.1

This release contains updated versions of 22 packages from GAP 4.9.1 distribution. Additionally, it has three new packages. The new JupyterKernel package by Markus Pfeiffer provides a so-called kernel for the Jupyter interactive document system (https://jupyter.org/). This package requires Jupyter to be installed on your system (see https://jupyter.org/install for instructions). It also requires GAP packages IO, ZeroMQInterface, json, and also two new packages by Markus Pfeiffer called crypting and uuid, all included into GAP 4.9.2 distribution. The JupyterKernel package is not yet usable on Windows.

#### 3.3 GAP 4.9.3 (September 2018)

##### 3.3-1 Changes in the core GAP system introduced in GAP 4.9.3

Fixed bugs that could lead to break loops:

- Fixed a regression in `HighestWeightModule` (Reference: HighestWeightModule) caused by changes in sort functions introduced in GAP 4.9 release (#2617).

Other fixed bugs and further improvements:

- Fixed a compile time assertion that caused compiler error on some systems (#2691).

##### 3.3-2 New and updated packages since GAP 4.9.2

This release contains updated versions of 18 packages from GAP 4.9.2 distribution. Additionally, it has three new packages:

- The curlInterface package by Christopher Jefferson and Michael Torpey, which provides a simple wrapper around libcurl library (https://curl.haxx.se/) to allow downloading files over http, ftp and https protocols.

- The datastructures package by Markus Pfeiffer, Max Horn, Christopher Jefferson and Steve Linton, which aims at providing standard datastructures, consolidating existing code and improving on it, in particular in view of HPC-GAP.

- The DeepThought package by Nina Wagner and Max Horn, which provides functionality for computations in finitely generated nilpotent groups given by a suitable presentation using Deep Thought polynomials.

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