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#############################################################################
##
## This file is part of GAP, a system for computational discrete algebra.
## This file's authors include Heiko Theißen, Ákos Seress.
##
## Copyright of GAP belongs to its developers, whose names are too numerous
## to list here. Please refer to the COPYRIGHT file for details.
##
## SPDX-License-Identifier: GPL-2.0-or-later
##

#############################################################################
##
#F StabChain( <G>[, <options>] )
#F StabChain( <G>, <base> )
#O StabChainOp( <G>, <options> )
#A StabChainMutable( <G> )
#A StabChainMutable( <permhomom> )
#A StabChainImmutable( <G> )
##
## <#GAPDoc Label="StabChain">
## <ManSection>
## <Func Name="StabChain" Arg='G[, options]'
## Label="for a group (and a record)"/>
## <Func Name="StabChain" Arg='G, base'
## Label="for a group and a base"/>
## <Oper Name="StabChainOp" Arg='G, options'/>
## <Attr Name="StabChainMutable" Arg='G'
## Label="for a group"/>
## <Attr Name="StabChainMutable" Arg='permhomom'
## Label="for a homomorphism"/>
## <Attr Name="StabChainImmutable" Arg='G'/>
##
## <Description>
## These commands compute a stabilizer chain for the permutation group
## <A>G</A>;
## additionally, <Ref Attr="StabChainMutable" Label="for a homomorphism"/>
## is also an attribute for the group homomorphism <A>permhomom</A>
## whose source is a permutation group.
## 
## (The mathematical background of stabilizer chains is sketched
## in <Ref Sect="Stabilizer Chains"/>,
## more information about the objects representing stabilizer chains
## in &GAP; can be found in <Ref Sect="Stabilizer Chain Records"/>.)
## 
## <Ref Oper="StabChainOp"/> is an operation with two arguments <A>G</A> and
## <A>options</A>,
## the latter being a record which controls some aspects of the computation
## of a stabilizer chain (see below);
## <Ref Oper="StabChainOp"/> returns a <E>mutable</E> stabilizer chain.
## <Ref Attr="StabChainMutable" Label="for a group"/> is a <E>mutable</E>
## attribute for groups or homomorphisms,
## its default method for groups is to call <Ref Oper="StabChainOp"/> with
## empty options record.
## <Ref Attr="StabChainImmutable"/> is an attribute with <E>immutable</E>
## values;
## its default method dispatches to
## <Ref Attr="StabChainMutable" Label="for a group"/>.
## 
## <Ref Func="StabChain" Label="for a group (and a record)"/> is a function
## with first argument a permutation group <A>G</A>,
## and optionally a record <A>options</A> as second argument.
## If the value of <Ref Attr="StabChainImmutable"/> for <A>G</A>
## is already known and if this stabilizer chain matches the requirements
## of <A>options</A>,
## <Ref Func="StabChain" Label="for a group (and a record)"/> simply returns
## this stored stabilizer chain.
## Otherwise <Ref Func="StabChain" Label="for a group (and a record)"/>
## calls <Ref Oper="StabChainOp"/> and returns an immutable copy of the
## result;
## additionally, this chain is stored as <Ref Attr="StabChainImmutable"/>
## value for <A>G</A>.
## If no <A>options</A> argument is given, its components default
## to the global variable <Ref Var="DefaultStabChainOptions"/>.
## If <A>base</A> is a list of positive integers,
## the version <C>StabChain( <A>G</A>, <A>base</A> )</C> defaults to
## <C>StabChain( <A>G</A>, rec( base:= <A>base</A> ) )</C>.
## 
## If given, <A>options</A> is a record whose components specify properties
## of the desired stabilizer chain or which may help the algorithm.
## Default values for all of them can be given in the global variable
## <Ref Var="DefaultStabChainOptions"/>.
## The following options are supported.
## <List>
## <C>base</C> (default an empty list)
## <Item>
## A list of points, through which the resulting stabilizer chain
## shall run.
## For the base <M>B</M> of the resulting stabilizer chain <A>S</A>
## this means the following.
## If the <C>reduced</C> component of <A>options</A> is <K>true</K> then
## those points of <C>base</C> with nontrivial basic orbits form the
## initial segment of <M>B</M>, if the <C>reduced</C> component is
## <K>false</K> then <C>base</C> itself is the initial segment of
## <M>B</M>.
## Repeated occurrences of points in <C>base</C> are ignored.
## If a stabilizer chain for <A>G</A> is already known then the
## stabilizer chain is computed via a base change.
## </Item>
## <C>knownBase</C> (no default value)
## <Item>
## A list of points which is known to be a base for the group.
## Such a known base makes it easier to test whether a permutation
## given as a word in terms of a set of generators is the identity,
## since it suffices to map the known base with each factor
## consecutively, rather than multiplying the whole permutations
## (which would mean to map every point).
## This speeds up the Schreier-Sims algorithm which is used when a new
## stabilizer chain is constructed;
## it will not affect a base change, however.
## The component <C>knownBase</C> bears no relation to the <C>base</C>
## component, you may specify a known base <C>knownBase</C> and a
## desired base <C>base</C> independently.
## </Item>
## <C>reduced</C> (default <K>true</K>)
## <Item>
## If this is <K>true</K> the resulting stabilizer chain <A>S</A> is
## reduced, i.e., the case <M>G^{(i)} = G^{(i+1)}</M> does not occur.
## Setting <C>reduced</C> to <K>false</K> makes sense only if
## the component <C>base</C> (see above) is also set;
## in this case all points of <C>base</C> will occur in the base
## <M>B</M> of <A>S</A>, even if they have trivial basic orbits.
## Note that if <C>base</C> is just an initial segment of <M>B</M>,
## the basic orbits of the points in <M>B \setminus </M><C>base</C>
## are always nontrivial.
## </Item>
## <C>tryPcgs</C> (default <K>true</K>)
## <Item>
## If this is <K>true</K> and either the degree is at most <M>100</M>
## or the group is known to be solvable, &GAP; will first try to
## construct a pcgs (see Chapter <Ref Chap="Polycyclic Groups"/>)
## for <A>G</A> which will succeed and implicitly construct a
## stabilizer chain if <A>G</A> is solvable.
## If <A>G</A> turns out non-solvable, one of the other methods will be
## used.
## This solvability check is comparatively fast, even if it fails,
## and it can save a lot of time if <A>G</A> is solvable.
## </Item>
## <C>random</C> (default <C>1000</C>)
## <Item>
## If the value is less than <M>1000</M>,
## the resulting chain is correct with probability
## at least <C>random</C><M> / 1000</M>.
## The <C>random</C> option is explained in more detail
## in <Ref Sect="Randomized Methods for Permutation Groups"/>.
## </Item>
## <C>size</C> (default <C>Size(<A>G</A>)</C> if this is known,
## i.e., if <C>HasSize(<A>G</A>)</C> is <K>true</K>)
## <Item>
## If this component is present, its value is assumed to be the order
## of the group <A>G</A>.
## This information can be used to prove that a non-deterministically
## constructed stabilizer chain is correct.
## In this case, &GAP; does a non-deterministic construction until the
## size is correct.
## </Item>
## <C>limit</C> (default <C>Size(Parent(<A>G</A>))</C> or
## <C>StabChainOptions(Parent(<A>G</A>)).limit</C>
## if it is present)
## <Item>
## If this component is present, it must be greater than or equal to
## the order of <A>G</A>.
## The stabilizer chain construction stops if size <C>limit</C> is
## reached.
## </Item>
## </List>
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction( "StabChain" );
DeclareOperation( "StabChainOp", [ IsGroup, IsRecord ] );
DeclareAttribute( "StabChainMutable", IsObject, "mutable" );
DeclareAttribute( "StabChainImmutable", IsObject );

#############################################################################
##
#A StabChainOptions( <G> )
##
## <#GAPDoc Label="StabChainOptions">
## <ManSection>
## <Attr Name="StabChainOptions" Arg='G'/>
##
## <Description>
## is a record that stores the options with which the stabilizer chain
## stored in <Ref Attr="StabChainImmutable"/> has been computed
## (see <Ref Func="StabChain" Label="for a group (and a record)"/>
## for the options that are supported).
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareAttribute( "StabChainOptions", IsPermGroup, "mutable" );

#############################################################################
##
#V DefaultStabChainOptions
##
## <#GAPDoc Label="DefaultStabChainOptions">
## <ManSection>
## <Var Name="DefaultStabChainOptions"/>
##
## <Description>
## are the options for
## <Ref Func="StabChain" Label="for a group (and a record)"/> which are set
## as default.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalName( "DefaultStabChainOptions" );

#############################################################################
##
#F StabChainBaseStrongGenerators( <base>, <sgs>[, <one>] )
##
## <#GAPDoc Label="StabChainBaseStrongGenerators">
## <ManSection>
## <Func Name="StabChainBaseStrongGenerators" Arg='base, sgs[, one]'/>
##
## <Description>
## Let <A>base</A> be a base for a permutation group <M>G</M>, and let
## <A>sgs</A> be a strong generating set for <M>G</M> with respect to
## <A>base</A>; <A>one</A> must be the appropriate identity element of
## <M>G</M> (see <Ref Attr="One"/>, in most cases this will be <C>()</C>).
## This function constructs a stabilizer chain corresponding to the given
## base and strong generating set without the need to find
## Schreier generators;
## so this is much faster than the other algorithms.
## 
## If <A>sgs</A> is nonempty, then the argument <A>one</A> is optional;
## if not given, then the <Ref Attr="One" Style="Text"/> of
## <C><A>sgs</A>[1]</C> is taken as the identity element.
## <Example><![CDATA[
## gap> sc := StabChainBaseStrongGenerators([1,2], [(1,3,4), (2,3,4)], ());
## <stabilizer chain record, Base [ 1, 2 ], Orbit length 4, Size: 12>
## gap> GroupStabChain(sc) = AlternatingGroup(4);
## true
## gap> StabChainBaseStrongGenerators([1,3], [(1,2),(3,4)]);
## <stabilizer chain record, Base [ 1, 3 ], Orbit length 2, Size: 4>
## ]]></Example>
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction( "StabChainBaseStrongGenerators" );

#############################################################################
##
#F CopyStabChain( <S> )
##
## <#GAPDoc Label="CopyStabChain">
## <ManSection>
## <Func Name="CopyStabChain" Arg='S'/>
##
## <Description>
## This function returns a mutable copy of the stabilizer chain <A>S</A>
## that has no mutable object (list or record) in common with <A>S</A>.
## The <C>labels</C> components of the result are possibly shared by several
## levels, but superfluous labels are removed.
## (An entry in <C>labels</C> is superfluous if it does not occur among the
## <C>genlabels</C> or <C>translabels</C> on any of the levels which share
## that <C>labels</C> component.)
## 
## This is useful for stabiliser sub-chains that have been obtained as
## the (iterated) <C>stabilizer</C> component of a bigger chain.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction( "CopyStabChain" );

#############################################################################
##
#F CopyOptionsDefaults( <G>, <options> ) . . . . . . . copy options defaults
##
## <#GAPDoc Label="CopyOptionsDefaults">
## <ManSection>
## <Func Name="CopyOptionsDefaults" Arg='G, options'/>
##
## <Description>
## sets components in a stabilizer chain options record <A>options</A>
## according to what is known about the group <A>G</A>.
## This can be used to obtain a new stabilizer chain for <A>G</A> quickly.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction( "CopyOptionsDefaults" );

#############################################################################
##
#F BaseStabChain( <S> )
##
## <#GAPDoc Label="BaseStabChain">
## <ManSection>
## <Func Name="BaseStabChain" Arg='S'/>
##
## <Description>
## returns the base belonging to the stabilizer chain <A>S</A>.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction( "BaseStabChain" );

#############################################################################
##
#A BaseOfGroup( <G> )
##
## <#GAPDoc Label="BaseOfGroup">
## <ManSection>
## <Attr Name="BaseOfGroup" Arg='G'/>
##
## <Description>
## returns a base of the permutation group <A>G</A>.
## There is <E>no</E> guarantee that a stabilizer chain stored in <A>G</A>
## corresponds to this base!
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareAttribute( "BaseOfGroup", IsPermGroup );

#############################################################################
##
#F SizeStabChain( <S> )
##
## <#GAPDoc Label="SizeStabChain">
## <ManSection>
## <Func Name="SizeStabChain" Arg='S'/>
##
## <Description>
## returns the product of the orbit lengths in the stabilizer chain
## <A>S</A>, that is, the order of the group described by <A>S</A>.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction( "SizeStabChain" );

#############################################################################
##
#F StrongGeneratorsStabChain( <S> )
##
## <#GAPDoc Label="StrongGeneratorsStabChain">
## <ManSection>
## <Func Name="StrongGeneratorsStabChain" Arg='S'/>
##
## <Description>
## returns a strong generating set corresponding to the stabilizer chain
## <A>S</A>.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction( "StrongGeneratorsStabChain" );

#############################################################################
##
#F GroupStabChain([<G>,] <S> )
##
## <#GAPDoc Label="GroupStabChain">
## <ManSection>
## <Func Name="GroupStabChain" Arg='[G,] S'/>
##
## <Description>
## constructs a permutation group with stabilizer chain <A>S</A>, i.e.,
## a group with generators <C>Generators( <A>S</A> )</C> to which <A>S</A>
## is assigned as component <C>stabChain</C>.
## If the optional argument <A>G</A> is given, the result will have the
## parent <A>G</A>.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction( "GroupStabChain" );

#############################################################################
##
#F IndicesStabChain( <S> )
##
## <#GAPDoc Label="IndicesStabChain">
## <ManSection>
## <Func Name="IndicesStabChain" Arg='S'/>
##
## <Description>
## returns a list of the indices of the stabilizers in the stabilizer
## chain <A>S</A>.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction( "IndicesStabChain" );

#############################################################################
##
#F ListStabChain( <S> )
##
## <#GAPDoc Label="ListStabChain">
## <ManSection>
## <Func Name="ListStabChain" Arg='S'/>
##
## <Description>
## returns a list that contains at position <M>i</M> the stabilizer of the
## first <M>i-1</M> base points in the stabilizer chain <A>S</A>.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction( "ListStabChain" );

#############################################################################
##
#F OrbitStabChain( <S>, <pnt> )
##
## <#GAPDoc Label="OrbitStabChain">
## <ManSection>
## <Func Name="OrbitStabChain" Arg='S, pnt'/>
##
## <Description>
## returns the orbit of <A>pnt</A> under the group described by the
## stabilizer chain <A>S</A>.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction( "OrbitStabChain" );

#############################################################################
##
#F ElementsStabChain( <S> )
##
## <#GAPDoc Label="ElementsStabChain">
## <ManSection>
## <Func Name="ElementsStabChain" Arg='S'/>
##
## <Description>
## returns a list of all elements of the group described by the stabilizer
## chain <A>S</A>. The list is duplicate free but may be unsorted.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction( "ElementsStabChain" );

#############################################################################
##
#F IteratorStabChain( <S> )
##
## <#GAPDoc Label="IteratorStabChain">
## <ManSection>
## <Func Name="IteratorStabChain" Arg='S'/>
##
## <Description>
## returns an iterator for the elements of the group described by the
## stabilizer chain <A>S</A>.
##
## The elements of the group <A>G</A> are produced by iterating through
## all base images in turn, and in the ordering induced by the base. For
## more details see <Ref Sect="Stabilizer Chains"/>
## </Description>
## </ManSection>
## <#/GAPDoc>
DeclareGlobalFunction( "NextIterator_StabChain" );
DeclareGlobalFunction( "IteratorStabChain" );

#############################################################################
##
#A MinimalStabChain(<G>)
##
## <#GAPDoc Label="MinimalStabChain">
## <ManSection>
## <Attr Name="MinimalStabChain" Arg='G'/>
##
## <Description>
## returns the reduced stabilizer chain corresponding to the base
## <M>[ 1, 2, 3, 4, \ldots ]</M>.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareAttribute( "MinimalStabChain", IsPermGroup );

#############################################################################
##
#F ChangeStabChain( <S>, <base>[, <reduced>] )
##
## <#GAPDoc Label="ChangeStabChain">
## <ManSection>
## <Func Name="ChangeStabChain" Arg='S, base[, reduced]'/>
##
## <Description>
## changes or reduces a stabilizer chain <A>S</A> to be adapted to the base
## <A>base</A>.
## The optional argument <A>reduced</A> is interpreted as follows.
## <List>
## <C>reduced = </C><K>false</K> : 
## <Item>
## change the stabilizer chain, do not reduce it,
## </Item>
## <C>reduced = </C><K>true</K> : 
## <Item>
## change the stabilizer chain, reduce it.
## </Item>
## </List>
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction( "ChangeStabChain" );

#############################################################################
##
#F ExtendStabChain( <S>, <base> )
##
## <#GAPDoc Label="ExtendStabChain">
## <ManSection>
## <Func Name="ExtendStabChain" Arg='S, base'/>
##
## <Description>
## extends the stabilizer chain <A>S</A> so that it corresponds to base
## <A>base</A>.
## The original base of <A>S</A> must be a subset of <A>base</A>.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction( "ExtendStabChain" );

#############################################################################
##
#F ReduceStabChain( <S> )
##
## <#GAPDoc Label="ReduceStabChain">
## <ManSection>
## <Func Name="ReduceStabChain" Arg='S'/>
##
## <Description>
## changes the stabilizer chain <A>S</A> to a reduced stabilizer chain by
## eliminating trivial steps.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction( "ReduceStabChain" );

#############################################################################
##
#F EmptyStabChain( <labels>, <id>[, <pnt>] )
##
## <#GAPDoc Label="EmptyStabChain">
## <ManSection>
## <Func Name="EmptyStabChain" Arg='labels, id[, pnt]'/>
##
## <Description>
## constructs a stabilizer chain for the trivial group with
## <C>identity</C> value equal to<A>id</A> and
## <C>labels = </C><M>\{ <A>id</A> \} \cup</M> <A>labels</A>
## (but of course with <C>genlabels</C> and <C>generators</C> values an
## empty list).
## If the optional third argument <A>pnt</A> is present, the only stabilizer
## of the chain is initialized with the one-point basic orbit
## <C>[ <A>pnt</A> ]</C> and with <C>translabels</C> and <C>transversal</C>
## components.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction( "EmptyStabChain" );

#############################################################################
##
#F ConjugateStabChain( <S>, <T>, <hom>, <map>[, <cond>] )
##
## <ManSection>
## <Func Name="ConjugateStabChain" Arg='S, T, hom, map[, cond]'/>
##
## <Description>
## conjugates the stabilizer chain <A>S</A>.
## If given, <A>cond</A> is a function that determines for a stabilizer
## record whether the recursion should continue for this record.
## </Description>
## </ManSection>
##
DeclareGlobalFunction( "ConjugateStabChain" );

#############################################################################
##
#F RemoveStabChain( <S> )
##
## <#GAPDoc Label="RemoveStabChain">
## <ManSection>
## <Func Name="RemoveStabChain" Arg='S'/>
##
## <Description>
## <A>S</A> must be a stabilizer record in a stabilizer chain.
## This chain then is cut off at <A>S</A> by changing the entries in
## <A>S</A>. This can be used to remove trailing trivial steps.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction( "RemoveStabChain" );

#############################################################################
##
#F TrimStabChain( <S>, <n> )
##
## <ManSection>
## <Func Name="TrimStabChain" Arg='S, n'/>
##
## <Description>
## This function trims all permutations in the stabilizer chain <A>S</A> to
## degree at most <A>n</A> (to save memory).
## </Description>
## </ManSection>
##
DeclareGlobalFunction( "TrimStabChain" );

DeclareOperation( "MembershipTestKnownBase", [ IsRecord, IsList, IsList ] );

#############################################################################
##
#F SiftedPermutation( <S>, <g> )
##
## <#GAPDoc Label="SiftedPermutation">
## <ManSection>
## <Func Name="SiftedPermutation" Arg='S, g'/>
##
## <Description>
## sifts the permutation <A>g</A> through the stabilizer chain <A>S</A>
## and returns the result after the last step.
## 
## The element <A>g</A> is sifted as follows: <A>g</A> is replaced by
## <C><A>g</A>
## * InverseRepresentative( <A>S</A>, <A>S</A>.orbit[1]^<A>g</A> )</C>,
## then <A>S</A> is replaced by <C><A>S</A>.stabilizer</C> and this process
## is repeated until <A>S</A> is trivial
## or <C><A>S</A>.orbit[1]^<A>g</A></C> is not in the basic orbit
## <C><A>S</A>.orbit</C>.
## The remainder <A>g</A> is returned, it is the identity permutation if and
## only if the original <A>g</A> is in the group <M>G</M> described by
## the original <A>S</A>.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction( "SiftedPermutation" );

#############################################################################
##
#F MinimalElementCosetStabChain( <S>, <g> )
##
## <#GAPDoc Label="MinimalElementCosetStabChain">
## <ManSection>
## <Func Name="MinimalElementCosetStabChain" Arg='S, g'/>
##
## <Description>
## Let <M>G</M> be the group described by the stabilizer chain <A>S</A>.
## This function returns a permutation <M>h</M> such that
## <M>G <A>g</A> = G h</M>
## (that is, <M><A>g</A> / h \in G</M>) and with the additional property that
## the list of images under <M>h</M> of the base belonging to <A>S</A> is
## minimal w.r.t. lexicographical ordering.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction( "MinimalElementCosetStabChain" );

#############################################################################
##
#F SCMinSmaGens(<G>,<S>,<emptyset>,<identity element>,<flag>)
##
## <ManSection>
## <Func Name="SCMinSmaGens" Arg='G,S,emptyset,identity element,flag'/>
##
## <Description>
## This function computes a stabilizer chain for a minimal base image and
## a smallest generating set w.r.t. this base for a permutation
## group.
## 
## <A>G</A> must be a permutation group and <A>S</A> a mutable stabilizer
## chain for <A>G</A> that defines a base <A>bas</A>.
## Let <A>mbas</A> the smallest image (OnTuples) of <A>G</A>.
## Then this operation changes <A>S</A> to a stabilizer chain w.r.t.
## <A>mbas</A>.
## The arguments <A>emptyset</A> and <A>identity element</A> are needed
## only for the recursion.
## 
## The function returns a record whose component <C>gens</C> is a list whose
## first element is the smallest element w.r.t. <A>bas</A>
## (i.e. an element which maps <A>bas</A> to <A>mbas</A>).
## If <A>flag</A> is <K>true</K>, <C>gens</C> is the smallest generating set
## w.r.t. <A>bas</A>.
## (If <A>flag</A> is <K>false</K> this will not be computed.)
## </Description>
## </ManSection>
##
DeclareGlobalFunction("SCMinSmaGens");

#############################################################################
##
#F LargestElementStabChain( <S>, <id> )
##
## <#GAPDoc Label="LargestElementStabChain">
## <ManSection>
## <Func Name="LargestElementStabChain" Arg='S, id'/>
##
## <Description>
## Let <M>G</M> be the group described by the stabilizer chain <A>S</A>.
## This function returns the element <M>h \in G</M> with the property that
## the list of images under <M>h</M> of the base belonging to <A>S</A> is
## maximal w.r.t. lexicographical ordering.
## The second argument must be an identity element (used to start the
## recursion).
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction( "LargestElementStabChain" );

DeclareCategory( "IsPermOnEnumerator",
 IsMultiplicativeElementWithInverse and IsPerm );

DeclareOperation( "PermOnEnumerator", [ IsList, IsObject ] );

DeclareGlobalFunction( "DepthSchreierTrees" );

#############################################################################
##
#F AddGeneratorsExtendSchreierTree( <S>, <new> )
##
## <#GAPDoc Label="AddGeneratorsExtendSchreierTree">
## <ManSection>
## <Func Name="AddGeneratorsExtendSchreierTree" Arg='S, new'/>
##
## <Description>
## adds the elements in <A>new</A> to the list of generators of <A>S</A>
## and at the same time extends the orbit and transversal.
## This is the only legal way to extend a Schreier tree
## (because this involves careful handling of the tree components).
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction( "AddGeneratorsExtendSchreierTree" );

DeclareGlobalFunction( "ChooseNextBasePoint" );
DeclareGlobalFunction( "StabChainStrong" );
DeclareGlobalFunction( "StabChainForcePoint" );
DeclareGlobalFunction( "StabChainSwap" );
DeclareGlobalFunction( "LabsLims" );

#############################################################################
##
#F InsertTrivialStabilizer( <S>, <pnt> )
##
## <#GAPDoc Label="InsertTrivialStabilizer">
## <ManSection>
## <Func Name="InsertTrivialStabilizer" Arg='S, pnt'/>
##
## <Description>
## <Ref Func="InsertTrivialStabilizer"/> initializes the current stabilizer
## with <A>pnt</A> as <Ref Func="EmptyStabChain"/> did,
## but assigns the original <A>S</A> to the new
## <C><A>S</A>.stabilizer</C> component, such that a new level with trivial
## basic orbit (but identical <C>labels</C> and <C>ShallowCopy</C>ed
## <C>genlabels</C> and <C>generators</C>) is inserted.
## This function should be used only if <A>pnt</A> really is fixed by the
## generators of <A>S</A>, because then new generators can be added and the
## orbit and transversal at the same time extended with
## <Ref Func="AddGeneratorsExtendSchreierTree"/>.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction( "InsertTrivialStabilizer" );

DeclareGlobalFunction( "InitializeSchreierTree" );

DeclareGlobalFunction( "BasePoint" );
DeclareGlobalFunction( "IsInBasicOrbit" );

#############################################################################
##
#F IsFixedStabilizer( <S>, <pnt> )
##
## <#GAPDoc Label="IsFixedStabilizer">
## <ManSection>
## <Func Name="IsFixedStabilizer" Arg='S, pnt'/>
##
## <Description>
## returns <K>true</K> if <A>pnt</A> is fixed by all generators of <A>S</A>
## and <K>false</K> otherwise.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction( "IsFixedStabilizer" );

#############################################################################
##
#F InverseRepresentative( <S>, <pnt> )
##
## <#GAPDoc Label="InverseRepresentative">
## <ManSection>
## <Func Name="InverseRepresentative" Arg='S, pnt'/>
##
## <Description>
## calculates the transversal element which maps <A>pnt</A> back to the base
## point of <A>S</A>. It just runs back through the Schreier tree from
## <A>pnt</A> to the root and multiplies the labels along the way.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction( "InverseRepresentative" );

DeclareGlobalFunction( "QuickInverseRepresentative" );
DeclareGlobalFunction( "InverseRepresentativeWord" );

DeclareGlobalFunction( "StabChainRandomPermGroup" );
DeclareGlobalFunction( "SCRMakeStabStrong" );
DeclareGlobalFunction( "SCRStrongGenTest" );
DeclareGlobalFunction( "SCRSift" );
DeclareGlobalFunction( "SCRStrongGenTest2" );
DeclareGlobalFunction( "SCRNotice" );
DeclareGlobalFunction( "SCRExtend" );
DeclareGlobalFunction( "SCRSchTree" );
DeclareGlobalFunction( "SCRRandomPerm" );
DeclareGlobalFunction( "SCRRandomString" );
DeclareGlobalFunction( "SCRRandomSubproduct" );
DeclareGlobalFunction( "SCRExtendRecord" );
DeclareGlobalFunction( "SCRRestoredRecord" );
DeclareGlobalFunction( "VerifyStabilizer" );
DeclareGlobalFunction( "VerifySGS" );
DeclareGlobalFunction( "ExtensionOnBlocks" );
DeclareGlobalFunction( "ClosureRandomPermGroup" );
#

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