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#############################################################################
##
## This file is part of GAP, a system for computational discrete algebra.
## This file's authors include Alexander Hulpke.
##
## 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
##
## This file contains declarations for the subgroup lattice functions for
## pc groups.
##

#############################################################################
##
#V InfoPcSubgroup
##
## <#GAPDoc Label="InfoPcSubgroup">
## <ManSection>
## <InfoClass Name="InfoPcSubgroup"/>
##
## <Description>
## Information function for the subgroup lattice functions using pcgs.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareInfoClass("InfoPcSubgroup");

#############################################################################
##
#O InvariantElementaryAbelianSeries( <G>, <morph>[, <N> [, <fine>]] )
##
## <#GAPDoc Label="InvariantElementaryAbelianSeries">
## <ManSection>
## <Func Name="InvariantElementaryAbelianSeries" Arg='G, morph[, N [, fine]]'/>
##
## <Description>
## For a (solvable) group <A>G</A> and a list of automorphisms <A>morph</A>
## of <A>G</A>, this command finds a normal series of <A>G</A> with
## elementary abelian factors such that every group in this series is
## invariant under every automorphism in <A>morph</A>.
## 
## If a normal subgroup <A>N</A> of <A>G</A> which is invariant under
## <A>morph</A> is given, this series is chosen to contain <A>N</A>.
## No tests are performed to check the validity of the arguments.
## 
## The series obtained will be constructed to prefer large steps unless
## <A>fine</A> is given as <K>true</K>.
## <Example><![CDATA[
## gap> g:=Group((1,2,3,4),(1,3));
## Group([ (1,2,3,4), (1,3) ])
## gap> hom:=GroupHomomorphismByImages(g,g,GeneratorsOfGroup(g),
## > [(1,4,3,2),(1,4)(2,3)]);
## [ (1,2,3,4), (1,3) ] -> [ (1,4,3,2), (1,4)(2,3) ]
## gap> InvariantElementaryAbelianSeries(g,[hom]);
## [ Group([ (1,2,3,4), (1,3) ]), Group([ (1,3)(2,4) ]), Group(()) ]
## ]]></Example>
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction("InvariantElementaryAbelianSeries");

#############################################################################
##
#O InducedAutomorphism( <epi>, <aut> )
##
## <#GAPDoc Label="InducedAutomorphism">
## <ManSection>
## <Func Name="InducedAutomorphism" Arg='epi, aut'/>
##
## <Description>
## Let <A>aut</A> be an automorphism of a group <M>G</M> and <A>epi</A> be
## a homomorphism from <M>G</M> to a group <M>H</M> such that the kernel of
## <A>epi</A> is fixed under <A>aut</A>.
## Let <M>U</M> be the image of <A>epi</A>.
## This command returns the automorphism of <M>U</M> induced by <A>aut</A>
## via <A>epi</A>, that is, the automorphism of <M>U</M> which maps
## <M>g</M><C>^<A>epi</A></C> to
## <C>(</C><M>g</M><C>^<A>aut</A>)^<A>epi</A></C>, for <M>g \in G</M>.
## <Example><![CDATA[
## gap> g:=Group((1,2,3,4),(1,2));
## Group([ (1,2,3,4), (1,2) ])
## gap> n:=Subgroup(g,[(1,2)(3,4),(1,3)(2,4)]);
## Group([ (1,2)(3,4), (1,3)(2,4) ])
## gap> epi:=NaturalHomomorphismByNormalSubgroup(g,n);
## [ (1,2,3,4), (1,2) ] -> [ f1*f2, f1 ]
## gap> aut:=InnerAutomorphism(g,(1,2,3));
## ^(1,2,3)
## gap> InducedAutomorphism(epi,aut);
## ^f2
## ]]></Example>
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction("InducedAutomorphism");

#############################################################################
##
#F InvariantSubgroupsElementaryAbelianGroup(<G>,<homs>[,<dims>]) submodules
##
## <#GAPDoc Label="InvariantSubgroupsElementaryAbelianGroup">
## <ManSection>
## <Func Name="InvariantSubgroupsElementaryAbelianGroup"
## Arg='G, homs[, dims]'/>
##
## <Description>
## Let <A>G</A> be an elementary abelian group
## and <A>homs</A> be a set of automorphisms of <A>G</A>.
## Then this function computes all subspaces of
## <A>G</A> which are invariant under all automorphisms in <A>homs</A>.
## When considering <A>G</A> as a module for the algebra generated by
## <A>homs</A>, these are all submodules.
## If <A>homs</A> is empty, it computes all subgroups.
## If the optional parameter <A>dims</A> is given, only submodules of this
## dimension are computed.
## <Example><![CDATA[
## gap> g:=Group((1,2,3),(4,5,6),(7,8,9));
## Group([ (1,2,3), (4,5,6), (7,8,9) ])
## gap> hom:=GroupHomomorphismByImages(g,g,[(1,2,3),(4,5,6),(7,8,9)],
## > [(7,8,9),(1,2,3),(4,5,6)]);
## [ (1,2,3), (4,5,6), (7,8,9) ] -> [ (7,8,9), (1,2,3), (4,5,6) ]
## gap> u:=InvariantSubgroupsElementaryAbelianGroup(g,[hom]);
## [ Group([ (7,8,9), (4,5,6), (1,2,3) ]),
## Group([ (1,3,2)(7,8,9), (1,3,2)(4,5,6) ]),
## Group([ (1,2,3)(4,5,6)(7,8,9) ]), Group(()) ]
## ]]></Example>
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction(
 "InvariantSubgroupsElementaryAbelianGroup");

#############################################################################
##
#F ActionSubspacesElementaryAbelianGroup(,<G>[,<dims>]) submodules
##
## <ManSection>
## <Func Name="ActionSubspacesElementaryAbelianGroup" Arg='P, G[, dims]'/>
##
## <Description>
## computes the permutation action of <A>P</A> on the subspaces of the
## elementary abelian subgroup <A>G</A> of <A>P</A>. Returns
## a list [<A>subspaces</A>,<A>action</A>], where <A>subspaces</A> is a list of all the
## subspaces and <A>action</A> a homomorphism from <A>P</A> in a permutation group,
## which is equal to the action homomrophism for the action of <A>P</A> on
## <A>subspaces</A>. If <A>dims</A> is given, only subspaces of dimension <A>dims</A> are
## considered.
## </Description>
## </ManSection>
##
DeclareGlobalFunction(
 "ActionSubspacesElementaryAbelianGroup");

#############################################################################
##
#F SubgroupsSolvableGroup(<G>[,<opt>]) . classreps of subgrps of <G>,
##
## <#GAPDoc Label="SubgroupsSolvableGroup">
## <ManSection>
## <Func Name="SubgroupsSolvableGroup" Arg='G[, opt]'/>
##
## <Description>
## This function (implementing the algorithm published in
## <Cite Key="Hulpke99"/>) computes subgroups of a solvable group <A>G</A>,
## using the homomorphism principle.
## It returns a list of representatives up to <A>G</A>-conjugacy.
## 
## The optional argument <A>opt</A> is a record, which may
## be used to suggest restrictions on the subgroups computed.
## The following record
## components of <A>opt</A> are recognized and have the following effects.
## Note that all of the following
## restrictions to subgroups with particular properties are
## only used to speed up the calculation, but the result might still contain
## subgroups (that had to be computed in any case) that do not satisfy the
## properties. If this is not desired, the calculation must be followed by an
## explicit test for the desired properties (which is not done by default, as
## it would be a general slowdown).
## The function guarantees that representatives of all subgroups that
## satisfy the properties are found, i.e. there can be only false positives.
## <List>
## <C>actions</C>
## <Item>
## must be a list of automorphisms of <A>G</A>. If given, only groups
## which are invariant under all these automorphisms are computed. The
## algorithm must know the normalizer in <A>G</A> of the group generated by
## <C>actions</C> (defined formally by embedding in the semidirect product of
## <A>G</A> with <A>actions</A>).
## This can be given in the component <C>funcnorm</C> and
## will be computed if this component is not given.
## </Item>
## <C>normal</C>
## <Item>
## if set to <K>true</K> only normal subgroups are guaranteed to be
## returned (though some of the returned subgroups might still be not
## normal).
## </Item>
## <C>consider</C>
## <Item>
## a function to restrict the groups computed. This must be a
## function of five parameters, <M>C</M>, <M>A</M>, <M>N</M>, <M>B</M>,
## <M>M</M>, that are interpreted as follows:
## The arguments are subgroups of a factor <M>F</M> of <A>G</A> in the
## relation <M>F \geq C > A > N > B > M</M>.
## <M>N</M> and <M>M</M> are normal subgroups.
## <M>C</M> is the full preimage of the normalizer of <M>A/N</M>
## in <M>F/N</M>.
## When computing modulo <M>M</M> and looking for subgroups <M>U</M> such
## that <M>U \cap N = B</M> and <M>\langle U, N \rangle = A</M>,
## this function is called.
## If it returns <K>false</K> then
## all potential groups <M>U</M> (and therefore all groups later arising
## from them) are disregarded. This can be used for example to compute only
## subgroups of certain sizes.
## 
## (<E>This is just a restriction to speed up computations. The function may
## still return (invariant) subgroups which don't fulfill this condition!</E>)
## This parameter is used to permit calculations of some subgroups if the
## set of all subgroups would be too large to handle.
## 
## The actual groups <M>C</M>, <M>A</M>, <M>N</M> and <M>B</M> which are
## passed to this function are not necessarily subgroups of <A>G</A>
## but might be subgroups of a proper factor group <M>F = <A>G</A>/H</M>.
## Therefore the <C>consider</C> function may
## not relate the parameter groups to <A>G</A>.
## </Item>
## <C>retnorm</C>
## <Item>
## if set to <K>true</K> the function not only returns a list <C>subs</C>
## of subgroups but also a corresponding list <C>norms</C> of normalizers
## in the form <C>[ subs, norms ]</C>.
## </Item>
## <C>series</C>
## <Item>
## is an elementary abelian series of <A>G</A> which will be used for
## the computation.
## </Item>
## <C>groups</C>
## <Item>
## is a list of groups to seed the calculation. Only subgroups of
## these groups are constructed.
## </Item>
## </List>
## <Example><![CDATA[
## gap> g:=Group((1,2,3),(1,2),(4,5,6),(4,5),(7,8,9),(7,8));
## Group([ (1,2,3), (1,2), (4,5,6), (4,5), (7,8,9), (7,8) ])
## gap> hom:=GroupHomomorphismByImages(g,g,
## > [(1,2,3),(1,2),(4,5,6),(4,5),(7,8,9),(7,8)],
## > [(4,5,6),(4,5),(7,8,9),(7,8),(1,2,3),(1,2)]);
## [ (1,2,3), (1,2), (4,5,6), (4,5), (7,8,9), (7,8) ] ->
## [ (4,5,6), (4,5), (7,8,9), (7,8), (1,2,3), (1,2) ]
## gap> l:=SubgroupsSolvableGroup(g,rec(actions:=[hom]));;
## gap> SortedList(List(l,Size));
## [ 1, 2, 3, 4, 6, 8, 9, 18, 27, 54, 108, 216 ]
## gap> Length(ConjugacyClassesSubgroups(g)); # to compare
## 162
## ]]></Example>
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction("SubgroupsSolvableGroup");

#############################################################################
##
#F SizeConsiderFunction(<size>) returns `consider' function
##
## <#GAPDoc Label="SizeConsiderFunction">
## <ManSection>
## <Func Name="SizeConsiderFunction" Arg='size'/>
##
## <Description>
## This function returns a function <C>consider</C> of five arguments
## that can be used in <Ref Func="SubgroupsSolvableGroup"/> for
## the option <C>consider</C> to compute subgroups whose sizes are divisible
## by <A>size</A>.
## <Example><![CDATA[
## gap> l:=SubgroupsSolvableGroup(g,rec(actions:=[hom],
## > consider:=SizeConsiderFunction(6)));;
## gap> SortedList(List(l,Size));
## [ 1, 3, 6, 9, 18, 27, 54, 108, 216 ]
## ]]></Example>
## 
## This example shows that in general the <C>consider</C> function does not
## provide a perfect filter.
## It is guaranteed that all subgroups fulfilling the
## condition are returned, but not all subgroups returned necessarily fulfill
## the condition.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction("SizeConsiderFunction");

#############################################################################
##
#F ExactSizeConsiderFunction(<size>) returns `consider' function
##
## <#GAPDoc Label="ExactSizeConsiderFunction">
## <ManSection>
## <Func Name="ExactSizeConsiderFunction" Arg='size'/>
##
## <Description>
## This function returns a function <C>consider</C> of five arguments
## that can be used in <Ref Func="SubgroupsSolvableGroup"/> for
## the option <C>consider</C> to compute subgroups whose sizes are exactly
## <A>size</A>.
## <Example><![CDATA[
## gap> l:=SubgroupsSolvableGroup(g,rec(actions:=[hom],
## > consider:=ExactSizeConsiderFunction(6)));;
## gap> SortedList(List(l,Size));
## [ 1, 3, 6, 9, 27, 54, 108, 216 ]
## ]]></Example>
## 
## Again, the <C>consider</C> function does not provide
## a perfect filter. It is guaranteed that all subgroups fulfilling the
## condition are returned, but not all subgroups returned necessarily fulfill
## the condition.
## </Description>
## </ManSection>
## <#/GAPDoc>
##
DeclareGlobalFunction("ExactSizeConsiderFunction");

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