Quelle permut.gi Sprache: unbekannt

#############################################################################
##
#W permut.gi Permutability GAP library ABB&ECL&RER
##
##
#Y Copyright (C) 2000-2018 Adolfo Ballester-Bolinches, Enric Cosme-Ll\'opez
#Y and Ramon Esteban-Romero
##
## This file contains methods for permutability
##

#############################################################################
##
#V PermutMaxTries
##
## Maximum number of random attempts of permutability checks before trying
## general methods
##

PermutMaxTries:=10;

#############################################################################
##
#M ArePermutableSubgroups( <G>, , <V> ) . . . . for finite groups
##
## Returns true if and <V> permute, false otherwise.
##

InstallMethod(ArePermutableSubgroups, "with three arguments <G>, , <V>, where and <V> are subgroups of <G>",
 [IsGroup and IsFinite,IsGroup and IsFinite,IsGroup and IsFinite],
 function(G,U,V)
 local bool1, bool2;
 if not IsSubgroup(G,U)
 or not IsSubgroup(G,V)
 then
 Error(" and <V> must be subgroups of <G>");
 fi;
 bool1:=HasParent(U) and IsSubgroup(Parent(U),G);
 bool2:=HasParent(V) and IsSubgroup(Parent(V),G);
 #
 # a shortcut when one of the subgroups is normal in its parent
 #
 if (bool1 and HasIsNormalInParent(U) and IsNormalInParent(U))
 or (bool2 and HasIsNormalInParent(V) and IsNormalInParent(V))
 then
 return true;

 #
 # a shortcut when one of the subgroups is permutable in its parent
 #
 elif (bool1 and HasIsPermutableInParent(U) and IsPermutableInParent(U))
 or (bool2 and HasIsPermutableInParent(V) and IsPermutableInParent(V))
 then
 return true;
 #
 # a shortcut when one of the subgroups is contained in the other
 #
 elif IsSubgroup(U,V) or IsSubgroup(V,U)
 then
 return true;
 #
 # the general case
 #
 else
 return Size(U)*Size(V)=Size(Intersection(U,V))*
 Size(Subgroup(G,Union(GeneratorsOfGroup(U),
 GeneratorsOfGroup(V))));
 fi;
end);

#
## With two parameters, both groups must be subgroups of a common group.
#

InstallOtherMethod(ArePermutableSubgroups, "with two arguments",
 [IsGroup and IsFinite, IsGroup and IsFinite],
 function(U,V)
 local G;
 if IsIdenticalObj(Parent(U), Parent(V))
 then
 return ArePermutableSubgroups(Parent(U),U,V);
 else
 return ArePermutableSubgroups(ClosureGroup(U,V),U,V);
 fi;
end);

#############################################################################
##
#M Permutizer( <G>, ) . . . . for finite groups
##
## Computes the permutizer of a subgroup U in G. This is the
## subgroup generated by all the cyclic subgroups of G which permute with U.
##
InstallMethod(PermutizerOp,"for finite groups", [IsGroup and IsFinite,
 IsGroup and IsFinite],
 function(g,h)
 local ele, llista,z,bool1, n,x;
 if not IsSubgroup(g,h)
 then
 Error("<h> must be a subgroup of <g>");
 fi;
 bool1:=IsSubgroup(Parent(h),g);
 #
 # If h is normal or permutable in g, it is easy to compute the permutizer.
 #
 if bool1 and HasIsNormalInParent(h) and IsNormalInParent(h)
 then
 return g;
 fi;
 if bool1 and HasIsPermutableInParent(h) and IsPermutableInParent(h)
 then
 return g;
 fi;
 if IsNormal(g,h)
 then
 return g;
 fi;
 if IsPermutable(g,h)
 then
 return g;
 fi;
 # We start with the normaliser, then we add elements
 n:=Normalizer(g,h);
 for x in g do
 if not x in n and ArePermutableSubgroups(g,h,Subgroup(g,[x]))
 then
 n:=ClosureSubgroup(n,Subgroup(g,[x]));
 fi;
 # if n=g, we stop adding elements.
 if n=g
 then
 break;
 fi;
 od;

 return n;
end);

#############################################################################
##
#M AllSubnormalSubgroups( <G> ) . . . . for a finite group
##
## The default method constructs the lattice of subnormal subgroups.
##
InstallMethod(AllSubnormalSubgroups, "for a finite group",
 [IsGroup and IsFinite],
 function(G)
 local sn0,asn,sn1,x;
 sn0:=NormalSubgroups(G);
 asn:=ShallowCopy(sn0);
 repeat
 sn1:=[];
 for x in sn0
 do
 Append(sn1, Filtered(NormalSubgroups(x),
 x-> not x in asn and not x in sn1));
 od;
 sn0:=sn1;
 Append(asn,sn1);
 until sn1=[];
 return asn;
end
);

#############################################################################
##
#F AllGeneratorsCyclicPGroup( <x>, p ) . . . . for a p-element <x> of a group
##
## This operation computes all generators of the cyclic group
## generated by the p-element <x>.
##
##

InstallGlobalFunction(AllGeneratorsCyclicPGroup,function(x,p)
 local z,t;
 return List(Filtered([1..Order(x)], z->(z mod p)<>0),
 t->x^t);
end
 );



#############################################################################
##
#M IsPermutable( <G>, <H> ) . . . . for groups
##
## This operation returns true if H is permutable in G, false otherwise.
## H is permutable in G when H permutes with all subgroups of G.
##
InstallMethod(IsPermutableOp, "for finite groups",
 [IsGroup and IsFinite, IsGroup and
 IsFinite],
 function(g,h)
 local elg,z,P,hg,epi,g1,h1,h1q,gensh1q,r,gensr,x,y,g1q,q,bool1,bool2,
 ccsg1q,ccsh1q,u,su,i;

 if not IsSubgroup(g,h)
 then
 Error("<h> must be a subgroup of <g>");
 fi;
 #
 # If the Why function has been computed, then use it.
 #
 bool1:=IsSubgroup(Parent(h), g);
 bool2:=IsSubgroup(g, Parent(h));
 if bool1 and HasOneSubgroupNotPermutingWithInParent(h)
 and OneSubgroupNotPermutingWithInParent(h)=fail
 then
 return true;
 elif
 bool2 and HasOneSubgroupNotPermutingWithInParent(h)
 and OneSubgroupNotPermutingWithInParent(h)<>fail
 then
 return false;
 fi;

 #
 # immediate methods: permutability is inherited by subgroups
 # and normal subgroups are permutable
 #
 if bool1
 and ((HasIsNormalInParent(h) and IsNormalInParent(h)) or
 (HasIsPermutableInParent(h) and IsPermutableInParent(h)))
 then
 return true;
 fi;
 if bool2
 and (HasIsPermutableInParent(h) and not IsPermutableInParent(h))
 then
 return false;
 fi;

 #
 # permutable subgroups are subnormal, S-permutable, and conjugate-permutable
 #
 if bool1
 then
 if (HasIsSPermutableInParent(h) and not IsSPermutableInParent(h)) or
 (HasIsConjugatePermutableInParent(h)
 and not IsConjugatePermutableInParent(h))
 then
 return false;
 fi;
 fi;
 #
 # normal subgroups are permutable. This check is cheaper than ours.
 #
 if IsNormal(g,h)
 then
 return true;
 fi;
 #
 # subgroups of Iwasawa nilpotent groups are permutable
 #
 if (IsPGroup(g) and (HasIsPTGroup(g) and IsPTGroup(g) or
 HasIsPTGroup(SylowSubgroup(g,PrimePGroup(g)))
 and IsPTGroup(SylowSubgroup(g,PrimePGroup(g)))))
 or
 (IsNilpotentGroup(g) and HasIsPTGroup(g) and IsPTGroup(g))
 or
 (IsNilpotentGroup(g) and
 ForAll(PrimesDividingSize(g),
 q->HasIsPTGroup(SylowSubgroup(g,q)) and
 IsPTGroup(SylowSubgroup(g,q))))
 then
 return true;
 fi;

 #
 # we check whether the subgroup permute with some random cyclic
 # subgroups
 #

 for i in [1..PermutMaxTries] do
 u:=Random(g);
 su:=Subgroup(g,[u]);
 if not ArePermutableSubgroups(g, su, h)
 then
 if bool1
 then
 SetOneSubgroupNotPermutingWithInParent(h, su);
 fi;
 return false;
 fi;
 od;


 #
 # permutable subgroups are subnormal
 #
 if not(IsSubnormal(g,h))
 then
 return false;
 fi;

 hg:=Core(g,h);
 epi:=NaturalHomomorphismByNormalSubgroup(g,hg);
 g1:=Image(epi);
 h1:=Image(epi,h);
 UseFactorRelation(g,hg,g1);

 #
 # permutable subgroups mod core are nilpotent (not difficult to check)
 #
 if not IsNilpotent(h1)
 then
 return false;
 fi;
 # permutable subgroups are hypercentrally embedded;
 # we check that the Sylow q-subgroup of h/h_g centralises
 # the Sylow r-subgroups of g/h_G for r <> q
 for q in PrimesDividingSize(h1)
 do
 h1q:=SylowSubgroup(h1,q);
 g1q:=SylowSubgroup(g1,q);
 UseFactorRelation(SylowSubgroup(g,q),hg,g1q);
 r:=PResidual(g1,q);
 gensh1q:=GeneratorsOfGroup(h1q);
 gensr:=GeneratorsOfGroup(r);
 # if not ForAll(gensh1q,x->ForAll(gensh1q,y->y^x=y))
 if not ForAll(gensr,x->ForAll(gensh1q,y->y^x=y))
 then
 return false;
 fi;
 od;
 ### Now we check that the Sylow $p$-subgroups of H/H_G
 ### permute with all cyclic $p$-subgroups of G/H_G

 for q in PrimesDividingSize(h1)
 do
 h1q:=SylowSubgroup(h1,q);
 g1q:=SylowSubgroup(g1,q);
 if not (HasIsPTGroup(g1q) and IsPTGroup(g1q)) then
 ccsg1q:=ConjugacyClassSubgroups(g1,g1q);
 ccsh1q:=ConjugacyClassSubgroups(g1,h1q);
 if Size(ccsg1q)<Size(ccsh1q) then
 elg:=Difference(Union(AsList(ccsg1q)),h1q);
 while elg<>[] do
 x:=elg[1];
 if not ArePermutableSubgroups(g1,h1q,Subgroup(g1,[x]))
 then
 return false;
 fi;
 elg:=Difference(elg,AllGeneratorsCyclicPGroup(x,q));
 od;
 else
 elg:=AsList(g1q);
 while elg<>[] do
 x:=elg[1];
 if not ForAll(ccsh1q,
 zz->ArePermutableSubgroups(g1,
 zz,Subgroup(g1,[x])))
 then
 return false;
 fi;
 elg:=Difference(elg,AllGeneratorsCyclicPGroup(x,q));
 od;
 fi;
 fi;
 od;
 return true;


end);

#############################################################################
##
#M OneSubgroupNotPermutingWith( <G>, <H> ) . . . . for groups
##
## This operation finds a subgroup of G which does not permute with H
## if such a subgroup exists, otherwise it returns fail.
##
##
InstallMethod(OneSubgroupNotPermutingWithOp, "for finite groups",
 [IsGroup and IsFinite, IsGroup and IsFinite],
 function(g,h)
 local csg,z,w,bool1,bool2;
 if not IsSubgroup(g,h)
 then
 Error("<h> must be a subgroup of <g>");
 fi;
 bool1:=IsSubgroup(Parent(h),g);
 bool2:=IsSubgroup(g,Parent(h));
 if bool1 and bool2 then
 if HasOneSylowSubgroupNotPermutingWithInParent(h) and
 OneSylowSubgroupNotPermutingWithInParent(h)<>fail
 then
 return OneSylowSubgroupNotPermutingWithInParent(h);
 fi;
 if HasOneConjugateSubgroupNotPermutingWithInParent(h) and
 OneConjugateSubgroupNotPermutingWithInParent(h)<>fail
 then
 return OneConjugateSubgroupNotPermutingWithInParent(h);
 fi;
 fi;
 if bool1 and HasOneSubgroupNotPermutingWithInParent(h)
 and OneSubgroupNotPermutingWithInParent(h)=fail
 then
 SetIsPermutableInParent(h,true);
 return fail;
 fi;
 if bool2 and HasOneSubgroupNotPermutingWithInParent(h)
 and OneSubgroupNotPermutingWithInParent(h)<>fail
 then
 SetIsPermutableInParent(h,false);
 return OneSubgroupNotPermutingWithInParent(h);
 fi;



 w:=First(Zuppos(g),z->not ArePermutableSubgroups(g,h,Subgroup(g,[z])));
 if bool1 and bool2
 then SetIsPermutableInParent(h,w=fail);
 fi;
 if w=fail
 then
 return fail;
 fi;
 return Subgroup(g,[w]);
end);

#############################################################################
##
#M PrimesDividingSize( <G> ) . . . . for groups
##
## This attribute gives a list of primes dividing the size of G. It
## has been borrowed from the GAP manual.
##
InstallMethod(PrimesDividingSize, "for finite groups", [IsGroup and
 IsFinite],
 G -> PrimeDivisors(Size(G)));

#############################################################################
##
#M OneFSubgroupNotPermutingWith( <G>, <H>, <F> ) . . . . for groups
##
## This operation returns fail if H permutes with all members of F
## (a list of subgroups of G); otherwise it returns a member of F which
## does not permute with H.
##

InstallGlobalFunction( OneFSubgroupNotPermutingWith, function(g, h, f)
 local t,bool1,bool2,cex;
 if not IsSubgroup(g,h)
 then
 Error("<h> must be a subgroup of <g>");
 fi;

 if not IsList(f) or ForAny(f, t->not IsSubgroup(g,t))
 then
 Error("<f> must be a list of subgroups of <g>");
 fi;

 bool1:=IsSubgroup(Parent(h),g);
 if bool1
 and
 (
 (HasIsPermutableInParent(h) and IsPermutableInParent(h))
 or
 (HasOneSubgroupNotPermutingWithInParent(h)
 and OneSubgroupNotPermutingWithInParent(h)=fail)
 )
 then
 return fail;
 fi;
 cex:=First(f, t->not ArePermutableSubgroups(g, h, t));
 bool2:=IsSubgroup(g,Parent(h));
 if cex<>fail and bool2 then
 if not HasIsPermutableInParent(h)
 then
 SetIsPermutableInParent(h,false);
 fi;
 if not HasOneSubgroupNotPermutingWithInParent(h)
 then
 SetOneSubgroupNotPermutingWithInParent(h,cex);
 fi;
 fi;
 return cex;
end
 );


#############################################################################
##
#M IsFPermutable( <G>, <H>, <F> ) . . . . for groups
##
## This operation returns true if a subgroup H of G permutes
## with all the members of F, where F is a list of subgroups of G.
##

InstallGlobalFunction( IsFPermutable, function(g,h,f)
 return OneFSubgroupNotPermutingWith(g,h,f)=fail;
end
 );

#############################################################################
##
#M SylowSubgroups( <G> ) . . . . for groups
##
## This attribute gives a list of one Sylow subgroup for every prime
## dividing the size of G
##

#For soluble groups, we get a Sylow system.
InstallMethod(SylowSubgroups, "for finite soluble groups",
 [IsGroup and IsFinite and IsSolvableGroup],
 function(g)
 return SylowSystem(g);
end);

# Otherwise, we simply compute a Sylow subgroup for each prime
# dividing the order of the group.
InstallMethod(SylowSubgroups, "for finite groups", [IsGroup and
 IsFinite],
 function(g)
 return List(PrimesDividingSize(g),p->SylowSubgroup(g,p));
end);

#############################################################################
##
#M OneSylowSubgroupNotPermutingWith( <G>, <H> ) . . . . for groups
##
## This operation finds a Sylow subgroup of G which does not permute
## with H if such a subgroup exists, otherwise it returns false.
##
##
InstallMethod(OneSylowSubgroupNotPermutingWithOp, "for finite groups",
 [IsGroup and IsFinite, IsGroup and IsFinite],
 function(g,h)
 local sylows,z,r,x,y;
 if not IsSubgroup(g,h)
 then
 Error("<h> must be a subgroup of <g>");
 fi;

 if IsNilpotentGroup(g)
 then
 SetIsPSTGroup(g,true);
 return fail ;
 elif HasIsPSTGroup(g) and IsPSTGroup(g) and IsSubnormal(g,h)
 then
 return fail;
 elif HasIsNormalInParent(h) and IsNormalInParent(h)
 then
 return fail;
 elif IsNormal(g,h)
 then
 return fail;
 elif HasIsPermutableInParent(h) and IsPermutableInParent(h)
 then
 return fail;
 elif IsPGroup(h) # h cannot be trivial at this stage
 then
 r:=PResidual(g,PrimePGroup(h));
 if ForAll(GeneratorsOfGroup(r),
 x->ForAll(GeneratorsOfGroup(h),y->y^x in h))
 then
 return fail;
 fi;
 fi;
 sylows:=Union(List(SylowSubgroups(g),z->ConjugateSubgroups(g,z)));
 return First(sylows,z->not ArePermutableSubgroups(g,h,z));
end);

#############################################################################
##
#M OneSystemNormalizerNotPermutingWith( <G>, <H> ) . . . . for groups
##
## This operation finds a system normalizer of the soluble groups G
## which does not permute with H if such a subgroup exists, fail otherwise.
##
##
InstallMethod(OneSystemNormalizerNotPermutingWithOp, "for finite soluble groups",
 [IsGroup and IsFinite and IsSolvableGroup, IsGroup and IsFinite],
 function(g,h)
 local sysnor,sysnors,z,bool1;
 if not IsSubgroup(g,h)
 then
 Error("<h> must be a subgroup of <g>");
 fi;

 bool1:=IsSubset(Parent(h),g);
 if HasIsPermutableInParent(h) and IsPermutableInParent(h) and bool1
 then
 return fail;
 else
sysnor:=SystemNormalizer(g);
 sysnors:=AsList(ConjugacyClassSubgroups(g,sysnor));
 return First(sysnors,z->not ArePermutableSubgroups(g,h,z));
 fi;
end);

#############################################################################
##
#M IsSPermutable( <G>, <H> ) . . . . for groups
##
## This operation returns true if a subgroup H of G is S-permutable,
## and false otherwise.
##
InstallMethod(IsSPermutableOp, "for finite groups",
 [IsGroup and IsFinite, IsGroup and
 IsFinite],
 function(g,h)
 local sylows,z,cex,hg,pi,hhg,hp,hghp,p,gens,gensp,gensr,r,y,x;
 if not IsSubgroup(g,h)
 then
 Error("<h> must be a subgroup of <g>");
 elif not(IsSubnormal(g,h))
 then
 return false;
 fi;
 if IsNormal(g,h)
 then
 return true;
 fi;
 if IsSubgroup(Parent(g),h) and HasIsPermutableInParent(h)
 and IsPermutableInParent(h)
 then
 return true;
 else
 hg:=Core(g,h);
 hhg:=h/hg;
 pi:=PrimesDividingSize(hhg);
 if not IsNilpotent(hhg)
 then
 return false;
 fi;
 for p in pi
 do
 hp:=SylowSubgroup(h,p);
 r:=PResidual(g,p);
 gensr:=GeneratorsOfGroup(r);
 gensp:=GeneratorsOfGroup(hp);
 gens:=Union(GeneratorsOfGroup(hg),gensp);
 hghp:=Subgroup(h,gens);
 if not ForAll(gensp,x->ForAll(gensr,y->x^y in hghp))
 then
 return false;
 fi;
 od;
 return true;
 fi;
end);

#############################################################################
##
#M IsSNPermutable( <G>, <H> ) . . . . for groups
##
## This operation returns true a subgroup H of a soluble group G
## is SN-permutable, and false otherwise.
## H is SN-permutable in G when H permutes with all system normalizers of G.
##
InstallMethod(IsSNPermutableOp, "for finite groups",
 [IsGroup and IsFinite, IsGroup and
 IsFinite],
 function(g,h)
 local sylows,z,cex;
 if not IsSolvableGroup(g)
 then
 Error("<g> must be a solvable group");
 fi;
 if not IsSubgroup(g,h)
 then
 Error("<h> must be a subgroup of <g>");
 fi;
 #
 # SN-permutable subgroups are subnormal.
 #
 if not(IsSubnormal(g,h)) then
 return false;
 fi;
 #
 # Permutable subgroups are SN-permutable.
 #
 if HasIsPermutableInParent(g) and IsPermutableInParent(g)
 then
 return true;
 else
 cex:=OneSystemNormalizerNotPermutingWith(g,h);
 return cex=fail;
 fi;
end);

#############################################################################
##
#M OneConjugateSubgroupNotPermutingWith( <G>, <H> ) . . . . for groups
##
## This operation finds a conjugate subgroup of H which does not permute
## with H if such a subgroup exists, otherwise it returns fail.
##

InstallMethod(OneConjugateSubgroupNotPermutingWithOp, "for finite groups",
 [IsGroup and IsFinite, IsGroup and IsFinite],
 function(G,H)
 local z,cex;
 if not IsSubgroup(G,H)
 then
 Error("<h> must be a subgroup of <g>");
 #
 # Permutable subgroups are conjugate-permutable.
 #
 elif HasIsPermutableInParent(H) and IsPermutableInParent(H)
 then
 return fail;
 else
 cex:=First(ConjugateSubgroups(G,H),
 z->not ArePermutableSubgroups(G,H,z));
 return cex;
 fi;
end);

#############################################################################
##
#M IsConjugatePermutable( <G>, <H> ) . . . . for groups
##
## This operation returns true if the subgroup H of G is
## conjugate-permutable, and false otherwise.
## H is conjugate-permutable in G when H permutes with H^g for every g of G.
##

InstallMethod(IsConjugatePermutableOp, "for finite groups",
 [IsGroup and IsFinite, IsGroup and IsFinite],
 function(G,H)
 local z,cex;
 if not IsSubgroup(G,H)
 then
 Error("<H> must be a subgroup of <G>");
 #
 # normal subgroups are conjugate-permutable
 #
 elif HasIsNormalInParent(H) and IsNormalInParent(H)
 then
 return true;
 else
 cex:=OneConjugateSubgroupNotPermutingWith(G,H);
 return cex=fail;
 fi;
end);

#############################################################################
##
#M OneElementShowingNotWeaklyNormal( <G>, <H> ) . . . . for groups
##
## This operation finds an element g of G such that H normal <H, H^g>
## but H not normal in <H,g> if such an element exists, fail otherwise.
## H is weakly normal in G when H normal in <H,H^g> implies H normal in <H,g>.
##

InstallMethod(OneElementShowingNotWeaklyNormalOp, "for finite groups",
 [IsGroup and IsFinite, IsGroup and IsFinite],
 function(g,h)
 local x,cex,n;
 n:=Normalizer(g,h);
 if not IsSubgroup(g,h)
 then
 Error("<h> must be a subgroup of <g>");
 fi;
 cex:=First(RightTransversal(g, n),
 x->IsSubgroup(n, ConjugateSubgroup(h,x))
 and not x in n);
 return cex;
end);

#############################################################################
##
#M IsWeaklyNormal( <G>, <H> ) . . . . for groups
##
## This operation returns true if a subgroup H of G is
## weakly normal, false otherwise.
## H is weakly normal when H^g\le N_G(H) implies g\in N_G(H)
##

InstallMethod(IsWeaklyNormalOp, "for finite groups",
 [IsGroup and IsFinite, IsGroup and IsFinite],
 function(g,h)
 local x,cex;
 cex:=OneElementShowingNotWeaklyNormal(g,h);
 return cex=fail;
end);

#############################################################################
##
#M OneElementShowingNotWeaklySPermutable( <G>, <H> ) . . . . for groups
##
## This operation finds an element g of G such that H Sper <H, H^g>
## but H not Sper <H,g> if such an element exists, fail otherwise.
## H is weakly S-permutable in G when H Sper <H,H^g> implies H Sper <H,g>.
##

InstallMethod(OneElementShowingNotWeaklySPermutableOp, "for finite groups",
 [IsGroup and IsFinite, IsGroup and IsFinite],
 function(g,h)
 local x,cex;
 if not IsSubgroup(g,h)
 then
 Error("<h> must be a subgroup of <g>");
 fi;
 cex:=First(RightTransversal(g,h),x->
 IsSPermutable(
 Subgroup(g,
 Union(
 GeneratorsOfGroup(h),
 GeneratorsOfGroup(
 ConjugateSubgroup(h,x))
 )),
 h
 )
 and not IsSPermutable(
 Subgroup(g,Union(GeneratorsOfGroup(h),[x])),
 h
 ));
 return cex;
end);

#############################################################################
##
#M IsWeaklySPermutable( <G>, <H> ) . . . . for groups
##
## This operation returns true if a subgroup H of G is
## weakly S-permutable, false otherwise.
## H is weakly S-permutable in G when H Sper <H,H^g> implies H Sper <H,g>.
##

InstallMethod(IsWeaklySPermutableOp, "for finite groups",
 [IsGroup and IsFinite, IsGroup and IsFinite],
 function(g,h)
 local x,cex;
 cex:=OneElementShowingNotWeaklySPermutable(g,h);
 return cex=fail;
end);

#############################################################################
##
#M OneElementShowingNotWeaklyPermutable( <G>, <H> ) . . . . for groups
##
## This operation find an element g such that H per <H, H^g> but
## H not per <H, g> if such an element exists, fail otherwise.
## H is permutable in G when H per <H,H^g> implies H per <H,g>.
##

InstallMethod(OneElementShowingNotWeaklyPermutableOp, "for finite groups", [IsGroup and
 IsFinite, IsGroup and IsFinite],
 function(g,h)
 local x;
 if not IsSubgroup(g,h)
 then
 Error("<h> must be a subgroup of <g>");
 fi;
 return First(RightTransversal(g,h),x->
 IsPermutable(
 Subgroup(g,
 Union(
 GeneratorsOfGroup(h),
 GeneratorsOfGroup(
 ConjugateSubgroup(h,x)
 )
 )
 ),
 h
 )
 and not IsPermutable(
 Subgroup(g,Union(GeneratorsOfGroup(h),[x])),
 h
 )
 );
end);

#############################################################################
##
#M IsWeaklyPermutable( <G>, <H> ) . . . . for groups
##
## This operation returns true if a subgroup H of G is
## weakly permutable, false otherwise.
## H is weakly permutable in G when H per <H, H^g> implies H per <H, g>.
##

InstallMethod(IsWeaklyPermutableOp, "for finite groups", [IsGroup and
 IsFinite, IsGroup and IsFinite],
 function(g,h)
 local x,cex;
 cex:=OneElementShowingNotWeaklyPermutable(g,h);
 return cex=fail;
end);

#############################################################################
##
#M OneSubnormalNonPermutableSubgroup( <G> ) . . . . for finite groups
##
## The default method finds a non conjugate-permutable subnormal subgroup
## of G if there exists one such subgroup, it returns fail otherwise.
##

InstallMethod(OneSubnormalNonPermutableSubgroup,"for finite PT-groups",
 [IsGroup and IsFinite and IsPTGroup],
 function(G)
 local z;
 return fail;
end);

InstallMethod(OneSubnormalNonPermutableSubgroup, "for finite groups with AllSubnormalSubgroups",
 [IsGroup and IsFinite and HasAllSubnormalSubgroups],
 function(G)
 local x;
 return First(AllSubnormalSubgroups(G),x->not IsPermutable(G,x));
end
 );

# If we do not know whether the group is a PT-group,
# we look for a subnormal subgroup which is not permutable.

InstallMethod(OneSubnormalNonPermutableSubgroup,"for finite groups non PT-groups",
 [IsGroup and IsFinite],
 function(G)
 local z,ex,ns,nsz,sns,t,new,sn1,sn0,w,asn,x;
 if HasOneSubnormalNonSPermutableSubgroup(G) and OneSubnormalNonSPermutableSubgroup(G)<>fail
 then
 return OneSubnormalNonSPermutableSubgroup(G);
 fi;
 if HasOneSubnormalNonConjugatePermutableSubgroup(G) and OneSubnormalNonConjugatePermutableSubgroup(G)<>fail
 then
 return OneSubnormalNonConjugatePermutableSubgroup(G);
 fi;
 sn0:=Set(NormalSubgroups(G));
 asn:=ShallowCopy(sn0);
 repeat
 sn1:=[];
 for x in sn0
 do
 new:=Filtered(NormalSubgroups(x),
 x->not x in asn and not x in sn1);
 w:=First(new,z->not IsPermutable(G,z));
 if w<>fail
 then
 SetIsPTGroup(G,false);
 SetIsTGroup(G,false);
 return w;
 fi;
 UniteSet(sn1,new);

 od;
 sn0:=sn1;
 UniteSet(asn,sn1);
 until sn1=[];
 SetAllSubnormalSubgroups(G,asn);
 SetIsPTGroup(G, true);
 SetIsCPTGroup(G, true);
 SetIsPSTGroup(G, true);
 SetIsPSNTGroup(G, true);
 return fail;
end);

#############################################################################
##
#M IsAbCp( <G>, ) . . . . for finite groups
##
## Returns true if the group has an abelian Sylow p-subgroup P and every
## subgroup of P is normalised by N_G(P), false otherwise.
##

InstallMethod(IsAbCpOp,
 "generic method for group and prime",
 [IsGroup and IsFinite,IsPosInt],
 function(G,p)
 local gN,P,a,n,c,e,nc,b,r,t,compiscps,pos,i,u;
 # if p does not divide |G|, it is true
 if (Size(G) mod p)<>0
 then
 return true;
 fi;
 P:=SylowSubgroup(G,p);
 if not IsAbelian(P)
 then
 return false;
 fi;
 # Now P is abelian. We check if being Cp is stored
 compiscps:=ComputedIsCps(G);
 pos:=Position(compiscps{[1,3..Length(compiscps)-1]},p);
 if pos<>fail
 then
 return IsAbCp(G,p);
 fi;

 if p=Minimum(PrimesDividingSize(G))
 then
 return IsPNilpotent(G,p);
 fi;
 n:=Normalizer(G,P);
 # we enforce this test before computing the discrete logarithm
 if ForAny(GeneratorsOfGroup(P),t->not IsNormal(n,Subgroup(G,[t])))
 then
 return false;
 fi;

 c:=Centralizer(G,P);
 if IsSubgroup(c,n)
 then
 return true;
 fi;
 e:=NaturalHomomorphismByNormalSubgroup(n,c);
 nc:=Image(e);
 if not IsCyclic(nc)
 then
 return false;
 fi;
 a:=First(GeneratorsOfGroup(P),t->Order(t)=Exponent(P));
 b:=PreImagesRepresentative(e,MinimalGeneratingSet(nc)[1]);
 r:=First([1..Exponent(P)-1],t->a^b=a^t);
 return ForAll(GeneratorsOfGroup(P),t->t^b=t^r);
end
 );

#############################################################################
##
#M IsDedekindSylow( <G>, ) . . . . for finite groups
##
## Returns true if a Sylow p-subgroup of G is Dedekind, else returns false
##

InstallGlobalFunction(IsDedekindSylow, function(G,p)
 local P,res,epi,a1,a2,mgs;
 P:=SylowSubgroup(G,p);
 if HasIsTGroup(P)
 then
 return IsTGroup(P);
 elif p>2 then
 res:=IsAbelian(P);
 SetIsTGroup(P,res);
 return res;
 else
 if IsAbelian(P)
 then
 SetIsTGroup(P,true);
 return true;
 else
 #
 # the group should be a direct product of
 # an elementary abelian group and a quaternion group
 #
 if Size(FrattiniSubgroup(P))<>2
 then
 SetIsTGroup(P,false);
 return false;
 elif Exponent(Centre(P))>2 or Index(P,Centre(P))<>4
 then
 SetIsTGroup(P,false);
 return false;
 else

 epi:=NaturalHomomorphismByNormalSubgroup(P,Centre(P));
 mgs:=MinimalGeneratingSet(Image(epi));
 a1:=PreImagesRepresentative(epi,mgs[1]);
 a2:=PreImagesRepresentative(epi,mgs[2]);
 if Order(a1)<>4 or Order(a2)<>4 then
 SetIsTGroup(P,false);
 return false;
 else
 SetIsTGroup(P,true);
 return true;
 fi;
 fi;

 fi;
 fi;
end
 );

#############################################################################
##
#M IsIwasawaSylow( <G>, ) . . . . for finite groups
##
## Returns true if a Sylow p-subgroup of G is modular, else returns false
##

InstallGlobalFunction(IsIwasawaSylow,function(G,p)
 local P,z,ex,x,l,l1,l2,res,u,v,gu,gv,i;
 P:=SylowSubgroup(G,p);
 if (HasIsPTGroup(P))
 then
 return IsPTGroup(P);
 elif IsAbelian(P)
 then
 SetIsTGroup(P,true);
 SetIsPTGroup(P,true);
 return true;
 else
 # first we check permutability of a few subgroup pairs
 for i in [1..PermutMaxTries] do
 u:=Random(P);
 v:=Random(P);
 gu:=Subgroup(P,[u]);
 gv:=Subgroup(P,[v]);
 if not ArePermutableSubgroups(P, gu, gv)
 then
 SetIsTGroup(P,false);
 SetIsPTGroup(P,false);
 SetOneSubnormalNonSPermutableSubgroup(P,gu);
 SetOneSubnormalNonPermutableSubgroup(P,gu);
 return false;
 fi;
 od;
 # Now we apply the general method
 res:=IwasawaTriple(P);
 if res=fail
 then
 SetIsTGroup(P, false);
 SetIsPTGroup(P,false);
 return false;
 elif res=[]
 then
 SetIsPTGroup(P,true);
 SetIsTGroup(P,true);
 return true;
 elif p=2
 then
 SetIsTGroup(P,false);
 SetIsPTGroup(P,res[3]<>1);
 return res[3]<>1;
 else
 SetIsTGroup(P,false);
 SetIsPTGroup(P,true);
 return true;
 fi;
 fi;
end
 );

#############################################################################
##
#M IsCp( <G>, ) . . . . for finite groups
##
## Returns true if every subgroup of a Sylow p-subgroup P of G
## is normalised by N_G(P), false otherwise.
##

InstallMethod(IsCpOp,
 "generic method for a finite group and prime",
 [IsGroup and IsFinite,IsPosInt],
 function(g,p)
 local a,compisabcp,pos,P;

 P:=SylowSubgroup(g,p);
 compisabcp:=ComputedIsAbCps(g);
 pos:=Position(compisabcp{[1,3..Length(compisabcp)-1]},p);
 if p<>fail then
 if IsAbCp(g,p)
 then
 return true;
 elif IsAbelian(P)
 then
 return false;
 fi;
 fi;
 return (IsPNilpotent(g,p) and IsDedekindSylow(g,p)) or IsAbCp(g,p);
end
);

#############################################################################
##
#M IsXp( <G>, ) . . . . for finite groups
##
## Returns true if every subgroup of a Sylow p-subgroup P of G
## is permutable in N_G(P), false otherwise.
##

InstallMethod(IsXpOp,
 "generic method for a finite group and a prime",
 [IsGroup and IsFinite,IsPosInt],
 function(g,p)
 local a,compisabcp,pos,P;

 P:=SylowSubgroup(g,p);
 compisabcp:=ComputedIsAbCps(g);
 pos:=Position(compisabcp{[1,3..Length(compisabcp)-1]},p);
 if p<>fail then
 if IsAbCp(g,p)
 then
 return true;
 fi;
 fi;
 return (IsPNilpotent(g,p) and IsIwasawaSylow(g,p)) or IsAbCp(g,p);
end
);

#############################################################################
##
#M IsYp( <G>, ) . . . . for finite groups
##
## Returns true if for every p-subgroups H and K such that $H\le K$,
## $H$ is S-permutable in N_G(K), false otherwise.
##
##

InstallMethod(IsYpOp,
 "generic method for group and prime",
 [IsGroup and IsFinite,IsPosInt],
 function(g,p)
 local a,compisabcp,pos,P;

 P:=SylowSubgroup(g,p);
 compisabcp:=ComputedIsAbCps(g);
 pos:=Position(compisabcp{[1,3..Length(compisabcp)-1]},p);
 if p<>fail then
 if IsAbCp(g,p)
 then
 return true;
 fi;
 fi;
 return IsPNilpotent(g,p) or IsAbCp(g,p);
end
);

#############################################################################
##
#F IwasawaTripleWithSubgroup( <G>, <X>, ) . . . . for finite groups
##
## Returns an Iwasawa triple of the p-group g such that x belongs to it
## if it exists one, fail otherwise.
##

InstallGlobalFunction(IwasawaTripleWithSubgroup,function(g,x,p)
 local a,b,c,d,e,h,s,t,res;
 ### We make sure that every generator spans a normal subgroup,
 ### otherwise there cannot be an Iwasawa triple
 if ForAny(GeneratorsOfGroup(x),t->not IsNormal(g,Subgroup(g,[t])))
 then
 return fail;
 fi;
 e:=NaturalHomomorphismByNormalSubgroup(g,x);
 h:=Image(e);
 b:=PreImagesRepresentative(e,MinimalGeneratingSet(h)[1]);
 a:=First(GeneratorsOfGroup(x),t->Order(t)=Exponent(x));
 # Print("a");
 for c in AllGeneratorsCyclicPGroup(b,p) do
 s:=First([1..Log(Order(a),p)],t->a^c=a^(1+p^t));
 # Print("#I c=", c,"\ts=",s,"\n");
 if s<>fail
 then
 res:=ForAll(GeneratorsOfGroup(x),t->t^c=t^(1+p^s));
 if res
 then
 return [x,c,s];
 fi;
 fi;
 od;
 return fail;
end
 );

#############################################################################
##
#M IwasawaTriple( <G> ) . . . . for finite groups
##
## Computes an Iwasawa triple for the p-group G
##

InstallMethod(IwasawaTriple,"for finite p-groups",
 [IsGroup and IsFinite],
 function(P)
 local p,z,ex,x,l,l1,l2,res;
 if not IsPGroup(P)
 then
 Error(" must be a p-group for a prime p");
 elif IsTrivial(P)
 then
 #
 # We use this arbitrarily chosen value
 # to avoid an error in the trivial case
 #
 return [P, Identity(P), 3];
 elif HasIsPTGroup(P) and not IsPTGroup(P)
 then
 # If we know that the group is not Iwasawa, there is no such triple
 return fail;
 else
 p:=PrimePGroup(P);
 if IsAbelian(P)
 then
 return [P,Identity(P),Log(Exponent(P),p)];
 elif not IsAbelian(DerivedSubgroup(P)) # group should be metabelian
 then
 return fail;
 elif p=2 and Exponent(P)=4
 then
 if IsTGroup(P) then return []; else return fail; fi;
 else
 # We apply Iwasawa's theorem by looking
 # for an abelian subgroup with cyclic quotient
 l:=[P];
 repeat
 x:=l[Length(l)];
 Unbind(l[Length(l)]);
 l1:=Filtered(MaximalSubgroups(x),
 t->IsNormal(P,t) and IsCyclic(P/t));
 l:=Concatenation(l1,l);
 l2:=Filtered(l1,IsAbelian);
 for x in l2
 do
 res:=IwasawaTripleWithSubgroup(P,x,p);
 if res<>fail
 then
 return res;
 fi;
 od;
 until l=[];
 return fail;
 fi;
 fi;
end);


#############################################################################
##
#M IsPTGroup( <G> ) . . . . for finite groups
##
## Returns true if the group is a PT-group, else returns false
##

InstallMethod(IsPTGroup,"for finite solvable groups",
 [IsGroup and IsFinite and IsSolvableGroup],
 function(G)
 local p;

 if HasIsPSTGroup(G) and not IsPSTGroup(G)
 then
 return false;
 elif HasIsCPTGroup(G) and not IsCPTGroup(G)
 then
 return false;
 elif IsSupersolvableGroup(G)
 #
 # for solvable groups, we use the property Yp + modular Sylow
 # subgroups
 #
 then
 return(ForAll(PrimesDividingSize(G),
 p->(IsPNilpotent(G,p) and IsIwasawaSylow(G,p))
 or IsAbCp(G,p)));
 else
 return false;
 fi;
end);

InstallMethod(IsPTGroup,"for finite groups",
 [IsGroup and IsFinite],
 function(G)
 local p;

 if HasIsPSTGroup(G) and not IsPSTGroup(G)
 then
 return false;
 fi;
 if HasIsCPTGroup(G) and not IsCPTGroup(G)
 then
 return false;
 fi;
 if IsSolvable(G)
 then
 return IsPTGroup(G);
 elif IsSCGroup(G)
 then
 #
 # we use the definition
 #
 return(OneSubnormalNonPermutableSubgroup(G)=fail);
 else
 return false;
 fi;
end);

#############################################################################
##
#M OneSubnormalNonSPermutableSubgroup( <G> ) . . . . for finite groups
##
## The default method finds a non S-permutable subnormal subgroup of G
## if such a subgroup exists, fail otherwise.
##

# If the group is a PST-group, return fail
InstallMethod(OneSubnormalNonSPermutableSubgroup,"for finite PST-groups",
 [IsGroup and IsFinite and IsPSTGroup],
 function(G)
 local z;
 return fail;
end);

# If we do not know whether the group is a PST-group,
# we try to find a subnormal subgroup of defect 2
# which is not S-permutable.

InstallMethod(OneSubnormalNonSPermutableSubgroup,"for finite groups non PST-groups",
 [IsGroup and IsFinite],
 function(G)
 local z,ex,ns,nsz,t;
 ns:=NormalSubgroups(G);
 for z in ns
 do
 nsz:=NormalSubgroups(z);
 ex:=First(nsz,t->not IsSPermutable(G,t));
 if ex<>fail
 then
 SetIsPTGroup(G, false);
 SetIsTGroup(G, false);
 SetIsPSTGroup(G, false);
 return ex;
 fi;
 od;
 SetIsPSTGroup(G, true);
 return fail;
end);

#############################################################################
##
#M OneSubnormalNonSNPermutableSubgroup( <G> ) . . . . for finite groups
##
## The default method finds a non SN-permutable subnormal
## (permutable with all system normalisers) subgroup
## of the soluble group G if such a subgroup exists, fail otherwise.
##

# If the group is a PSNT-group, return fail.

InstallMethod(OneSubnormalNonSNPermutableSubgroup,"for finite PSNT-groups",
 [IsGroup and IsFinite and IsSolvableGroup and IsPSNTGroup],
 function(G)
 local z;
 return fail;
end);

# If we do not know whether the group is a PSNT-group,
# we try to find a subnormal subgroup
# which is not S-permutable.

InstallMethod(OneSubnormalNonSNPermutableSubgroup,"for finite groups",
 [IsGroup and IsFinite],
 function(G)
 local z,ex,ns,nsz,sns,d,t;
 if not IsSolvableGroup(G)
 then
 Error("<G> must be a solvable group");
 fi;
 sns:=AllSubnormalSubgroups(G);
 d:=SystemNormalizer(G);
 ex:=First(sns,t->not ArePermutableSubgroups(G,d,t));
 if ex<>fail
 then
 SetIsPSNTGroup(G, false);
 else
 SetIsPSNTGroup(G, true);
 fi;
 return ex;

end);

#############################################################################
##
#M IsPSTGroup( <G> ) . . . . for finite groups
##
## Returns true if the group is a PST-group, else returns false
##

InstallMethod(IsPSTGroup,"for finite solvable groups",
 [IsGroup and IsFinite and IsSupersolvableGroup],
 function(G)
 local p;
 #
 # For finite soluble groups, we characterise it via Yp for all primes p:
 # p-nilpotent or abelian with Cp
 #
 return ForAll(PrimesDividingSize(G),
 p->IsPNilpotent(G,p) or IsAbCp(G,p));
end);

InstallMethod(IsPSTGroup,"for finite groups",
 [IsGroup and IsFinite],
 function(G)
 local p;
 #
 # For finite soluble groups, we characterise it via Yp for all primes p:
 # p-nilpotent or abelian with Cp
 #
 if IsSolvable(G)
 then
 if not IsSupersolvableGroup(G)
 then
 return false;
 else
 return IsPSTGroup(G);
 fi;
 else
 if not IsSCGroup(G)
 then
 return false;
 else
 #
 # For non-solvable groups, we use the definition
 #
 return (OneSubnormalNonSPermutableSubgroup(G)=fail);
 fi;
 fi;
end);

#############################################################################
##
#M IsPSNTGroup( <G> ) . . . . for finite groups
##
## Returns true if the soluble group is a PSNT-group, else returns false
## A soluble group is a PSNT-group if permutability with system
## normalisers is transitive.
##

InstallMethod(IsPSNTGroup, "for finite groups",
 [IsGroup and IsFinite],
 function(G)
 if IsSolvableGroup(G)
 then
 return (OneSubnormalNonSNPermutableSubgroup(G)=fail);
 else
 Error("<G> must be a solvable group");
 fi;
end
 );

#############################################################################
##
#M OneSubnormalNonConjugatePermutableSubgroup( <G> ) . . . . for finite groups
##
## The default method finds a non conjugate-permutable subnormal subgroup
## of G if such a subgroup exists, fail otherwise.
##

# If the group is CPT, then return fail
InstallMethod(OneSubnormalNonConjugatePermutableSubgroup,"for finite CPT-groups",
 [IsGroup and IsFinite and IsCPTGroup],
 function(G)
 local z;
 return fail;
end);

# If we do not know whether the group is CPT, the same check would be valid
InstallMethod(OneSubnormalNonConjugatePermutableSubgroup,"for finite groups with AllSubnormalSubgroups",
 [IsGroup and IsFinite and HasAllSubnormalSubgroups],
 function(G)
 local z,ex;

 ex:=First(AllSubnormalSubgroups(G),z->not IsConjugatePermutable(G,z));
# Now it is easy to know whether the group is CPT
 if (ex=fail)
 then
 SetIsCPTGroup(G,true);
 else
 SetIsCPTGroup(G,false);
 fi;
 return ex;
end);

# If we do not know whether the group is a CPT-group,
# we look for a subnormal subgroup which is not conjugate-permutable.

InstallMethod(OneSubnormalNonConjugatePermutableSubgroup,"for finite groups non CPT-groups",
 [IsGroup and IsFinite],
 function(G)
 local z,ex,ns,nsz,sns,t,new,sn1,sn0,w,asn,x;

 sn0:=Set(NormalSubgroups(G));
 asn:=ShallowCopy(sn0);
 repeat
 sn1:=[];
 for x in sn0
 do
 new:=Filtered(NormalSubgroups(x),
 x->not x in asn and not x in sn1);
 w:=First(new,z->not IsConjugatePermutable(G,z));
 if w<>fail
 then
 SetIsCPTGroup(G,false);
 SetIsPTGroup(G,false);
 SetIsTGroup(G,false);
 SetOneSubnormalNonPermutableSubgroup(G,w);
 SetOneSubnormalNonNormalSubgroup(G,w);
 return w;
 fi;
 UniteSet(sn1,new);

 od;
 sn0:=sn1;
 UniteSet(asn,sn1);
 until sn1=[];
 SetAllSubnormalSubgroups(G,asn);
 SetIsCPTGroup(G, true);
 return fail;
end);

#############################################################################
##
#M IsCPTGroup( <G> ) . . . . for finite groups
##
## Returns true if the group is a CPT-group (every subnormal subgroup
## is conjugate-permutable), else returns false
##

# For finite groups in general, we use the definition
InstallMethod(IsCPTGroup,"for finite groups",
 [IsGroup and IsFinite],
 function(G)
 local z,ex;
 ex:=OneSubnormalNonConjugatePermutableSubgroup(G);
 return (ex=fail);
end);

#############################################################################
##
#M OneSubnormalNonNormalSubgroup( <G> ) . . . . for finite groups
##
## The default method finds a non-normal subnormal subgroup of G
## if such a subgroup exists, otherwise returns false.
##

InstallMethod(OneSubnormalNonNormalSubgroup, "for finite groups with AllSubnormalSubgroups",
 [IsGroup and IsFinite and HasAllSubnormalSubgroups],
 function(G)
 local x;
 return Difference(AllSubnormalSubgroups(G),NormalSubgroups(G))=[];
end
 );

InstallMethod(OneSubnormalNonNormalSubgroup,"for finite groups non T-groups",
 [IsGroup and IsFinite],
 function(G)
 local z,ex,ns,nsz,t;
 ns:=NormalSubgroups(G);
 for z in ns
 do
 nsz:=NormalSubgroups(z);
 ex:=First(nsz,t->not IsNormal(G,t));
 if ex<>fail
 then
 SetIsTGroup(G, false);
 return ex;
 fi;
 od;
 SetIsTGroup(G, true);
 return fail;
end);

#############################################################################
##
#M IsTGroup( <G> ) . . . . for finite groups
##
## Returns true if the group is a T-group, else returns false
##

InstallMethod(IsTGroup,"for finite solvable groups",
 [IsGroup and IsFinite and IsSolvableGroup],
 function(G)
 local p;
 #
 # For finite soluble groups, we characterise it via Cp for all primes p:
 # p-nilpotent or abelian with Cp + Sylow Dedekind
 #
 if IsSupersolvableGroup(G)
 then
 return ForAll(PrimesDividingSize(G),
## p->(IsPERMUTPNilpotent(G,p) and IsDedekindSylow(G,p))
 p->(IsPNilpotent(G,p) and IsDedekindSylow(G,p))
 or IsAbCp(G,p));
 else
 return false;
 fi;
end);

InstallMethod(IsTGroup,"for finite groups",
 [IsGroup and IsFinite],
 function(G)
 local p;
 #
 # For finite soluble groups, we characterise it via Cp for all primes p:
 # p-nilpotent or abelian with Cp + Sylow Dedekind
 #
 if IsSolvable(G)
 then
 return IsPSTGroup(G);
 elif IsSCGroup(G)
 then

 #
 # For non-solvable groups, we use the definition
 #
 return (OneSubnormalNonNormalSubgroup(G)=fail);
 else
 return false;
 fi;
end);

#############################################################################
#############################################################################
##
#M IsSCGroup( <G> ) . . . . for finite groups
##
## Returns true if the group is an SC-group, and false otherwise.
## A group is an SC-group if all its chief factors are simple.
##
##

InstallMethod(IsSCGroup, "for finite solvable groups",
 [IsGroup and IsFinite and IsSolvableGroup],
 function(g)
 return IsSupersolvableGroup(g);
end
 );

InstallMethod(IsSCGroup, "for finite groups with chief series",
 [IsGroup and IsFinite and HasChiefSeries],
 function(g)
 local cs,j,fact;
 cs:=ChiefSeries(g);
 fact:=List([1..Length(cs)-1],j->cs[j]/cs[j+1]);
 return ForAll(fact,IsSimple);
end
 );

InstallMethod(IsSCGroup, "generic method for a finite group",
 [IsGroup and IsFinite],
 function(g)
 local cs;
 if IsSolvable(g)
 then
 return IsSupersolvableGroup(g);
 else
 cs:=ChiefSeries(g);
 return IsSCGroup(g);
 fi;
end
 );

#############################################################################
##
#M OneSubgroupInWhichSubnormalNotNormal( <G>, <H> ) . . . . for groups
##
## This operation finds a subgroup K of G such that H is subnormal in K,
## but H is not normal in K if such a subgroup exists, it returns fail otherwise.
## H satisfies the subnormalizer condition in G when H subnormal in K
## implies that H is normal in K.
##

InstallMethod(OneSubgroupInWhichSubnormalNotNormalOp, "for finite groups",
 [IsGroup and IsFinite, IsGroup and IsFinite ],
 function(g,h)
 local x,int,t,cex,bool1,bool2;
 if not IsSubgroup(g,h)
 then
 Error("<h> must be a subgroup of <g>");
 fi;

 bool1:=IsSubgroup(Parent(h),g);
 if
 (bool1 and HasIsWithSubnormalizerConditionInParent(h) and
 IsWithSubnormalizerConditionInParent(h))
 then
 return fail;
 fi;
 if IsNormal(g,h)
 then
 return fail;
 fi;

 if IsSubnormal(g,h) then
 #
 # it cannot be normal in g
 #
 return g;
 fi;

 bool2:=IsSubgroup(g,Parent(h));
 if (bool2 and HasOneSubgroupInWhichSubnormalNotNormalInParent(h)
 and OneSubgroupInWhichSubnormalNotNormalInParent(h)<>fail)
 then
 return OneSubgroupInWhichSubnormalNotNormalInParent(h);
 fi;
 int:=IntermediateSubgroups(g,h);
 cex:=First(int.subgroups, t->not IsNormal(t,h) and IsSubnormal(t,h));
 if bool1 and bool2 then
 if cex=fail
 then
 SetIsWithSubnormalizerConditionInParent(h,true);
 SetIsWithSubpermutizerConditionInParent(h,true);
 SetIsWithSSubpermutizerConditionInParent(h,true);
 fi;
 fi;
 return cex;

end
 );

#############################################################################
##
#M IsWithSubnormalizerCondition( <G>, <H> ) . . . . for groups
##
##
## This operation returns true if H satisfies the subnormaliser
## condition in G, false otherwise.
## H satisfies the subnormalizer condition in G when H subnormal in K
## implies that H is normal in K.
##

InstallMethod(IsWithSubnormalizerConditionOp, "for finite groups",
 [IsGroup and IsFinite, IsGroup and IsFinite],
 function(g,h)
 local bool1,bool2;
 if not IsSubgroup(g,h)
 then
 Error("<h> must be a subgroup of <g>");
 fi;
 bool1:=IsSubgroup(Parent(h),g);
 if bool1 and
 (
 (HasOneSubgroupInWhichSubnormalNotNormalInParent(h) and
 OneSubgroupInWhichSubnormalNotNormalInParent(h)=fail)
 or
 (HasIsWithSubnormalizerConditionInParent(h) and
 IsWithSubnormalizerConditionInParent(h))
 )
 then
 return true;
 fi;
 bool2:=IsSubgroup(g,Parent(h));
 if bool2 and
 (
 (HasOneSubgroupInWhichSubnormalNotNormalInParent(h) and
 OneSubgroupInWhichSubnormalNotNormalInParent(h)<>fail)
 or
 (HasOneSubgroupInWhichSubnormalNotPermutableInParent(h) and
 OneSubgroupInWhichSubnormalNotPermutableInParent(h)<>fail)
 or
 (HasOneSubgroupInWhichSubnormalNotSPermutableInParent(h) and
 OneSubgroupInWhichSubnormalNotSPermutableInParent(h)<>fail)
 or
 (HasIsWithSubnormalizerConditionInParent(h) and
 not IsWithSubnormalizerConditionInParent(h))
 or
 (HasIsWithSubpermutizerConditionInParent(h) and
 not IsWithSubpermutizerConditionInParent(h))
 or
 (HasIsWithSSubpermutizerConditionInParent(h) and
 not IsWithSSubpermutizerConditionInParent(h))
 )
 then
 return false;
 fi;
 return OneSubgroupInWhichSubnormalNotNormal(g,h)=fail;
end
 );

#############################################################################
##
#M OneSubgroupInWhichSubnormalNotPermutable( <G>, <H> ) . . . . for groups
##
## This operation finds a subgroup K of G such that H is subnormal in K,
## but H is not permutable in K if such a subgroup exists,
## otherwise it returns fail.
## H satisfies the subpermutizer condition in G when H subnormal in K
## implies that H is permutable in K.
##

InstallMethod(OneSubgroupInWhichSubnormalNotPermutableOp, "for finite groups",
 [IsGroup and IsFinite, IsGroup and IsFinite ],
 function(g,h)
 local x,int,t,cex,bool1,bool2;

 if not IsSubgroup(g,h)
 then
 Error("<h> must be a subgroup of <g>");
 fi;
 bool1:=IsSubgroup(Parent(h),g);
 if bool1 and
 (
 (HasIsWithSubnormalizerConditionInParent(h) and
 IsWithSubnormalizerConditionInParent(h))
 or
 (HasIsWithSubpermutizerConditionInParent(h) and
 IsWithSubpermutizerConditionInParent(h))
 )
 then
 return fail;
 fi;
 if IsNormal(g,h) or
 IsPermutable(g,h)
 then
 return fail;
 fi;

 if IsSubnormal(g,h) then
 #
 # h cannot be permutable in g
 #
 return g;
 fi;
 bool2:=IsSubgroup(g,Parent(h));
 if bool2 then
 if
 (HasOneSubgroupInWhichSubnormalNotPermutableInParent(h)
 and OneSubgroupInWhichSubnormalNotPermutableInParent(h)<>fail)
 then

 return OneSubgroupInWhichSubnormalNotPermutableInParent(h);
 elif
 (HasOneSubgroupInWhichSubnormalNotSPermutableInParent(h)
 and OneSubgroupInWhichSubnormalNotSPermutableInParent(h)<>fail)
 then

 return OneSubgroupInWhichSubnormalNotSPermutableInParent(h);
 fi;
 fi;

 int:=IntermediateSubgroups(g,h);

 cex:=First(int.subgroups, t->not IsNormal(t,h) and IsSubnormal(t,h));
 if bool1 and bool2 then
 if cex=fail
 then
 SetIsWithSubpermutizerConditionInParent(h,true);
 SetIsWithSSubpermutizerConditionInParent(h,true);
 else
 SetIsWithSubpermutizerConditionInParent(h,false);
 SetIsWithSubnormalizerConditionInParent(h,false);
 fi;
 fi;
 return cex;

end
 );

#############################################################################
##
#M IsWithSubpermutizerCondition( <G>, <H> ) . . . . for groups
##
##
## This operation returns true if H satisfies the subpermutiser condition
## in G, otherwise it returns false.
## H satisfies the subpermutizer condition in G when H subnormal in K
## implies that H is permutable in K.
##

InstallMethod(IsWithSubpermutizerConditionOp, "for finite groups",
 [IsGroup and IsFinite, IsGroup and IsFinite],
 function(g,h)
 local bool1,bool2;
 if not IsSubgroup(g,h)
 then
 Error("<h> must be a subgroup of <g>");
 fi;

 bool1:=IsSubgroup(Parent(h),g);
 if bool1 and
 (
 (HasOneSubgroupInWhichSubnormalNotNormalInParent(h) and
 OneSubgroupInWhichSubnormalNotNormalInParent(h)=fail)
 or
 (HasIsWithSubnormalizerConditionInParent(h) and
 IsWithSubnormalizerConditionInParent(h))
 or
 (HasOneSubgroupInWhichSubnormalNotPermutableInParent(h) and
 OneSubgroupInWhichSubnormalNotPermutableInParent(h)=fail)
 or
 (HasIsWithSubpermutizerConditionInParent(h) and
 IsWithSubpermutizerConditionInParent(h))
 )
 then
 return true;
 fi;
 bool2:=IsSubgroup(g,Parent(h));
 if bool2 and
 (
 (HasOneSubgroupInWhichSubnormalNotPermutableInParent(h) and
 OneSubgroupInWhichSubnormalNotPermutableInParent(h)<>fail)
 or
 (HasOneSubgroupInWhichSubnormalNotSPermutableInParent(h) and
 OneSubgroupInWhichSubnormalNotSPermutableInParent(h)<>fail)
 or
 (HasIsWithSubpermutizerConditionInParent(h) and
 not IsWithSubpermutizerConditionInParent(h))
 or
 (HasIsWithSSubpermutizerConditionInParent(h) and
 not IsWithSSubpermutizerConditionInParent(h))
 )
 then
 return false;
 fi;
 return OneSubgroupInWhichSubnormalNotPermutable(g,h)=fail;
end
 );

#############################################################################
##
#M OneSubgroupInWhichSubnormalNotSPermutable( <G>, <H> ) . . . . for groups
##
## This operation finds a subgroup K of G such that H is subnormal in K,
## but H is not S-permutable in K if such a subgroup exists,
## otherwise it returns fail.
## H satisfies the S-subpermutizer condition in G when H subnormal in K
## implies that H is S-permutable in K.
##

InstallMethod(OneSubgroupInWhichSubnormalNotSPermutableOp, "for finite groups",
 [IsGroup and IsFinite, IsGroup and IsFinite ],
 function(g,h)
 local x,int,t,cex,bool1,bool2;
 if not IsSubgroup(g,h)
 then
 Error("<h> must be a subgroup of <g>");
 fi;

 bool1:=IsSubgroup(Parent(h),g);
 if bool1 and
 (
 (HasIsWithSubnormalizerConditionInParent(h) and
 IsWithSubnormalizerConditionInParent(h))
 or
 (HasIsWithSubpermutizerConditionInParent(h) and
 IsWithSubpermutizerConditionInParent(h))
 or
 (HasIsWithSSubpermutizerConditionInParent(h) and
 IsWithSSubpermutizerConditionInParent(h))
 or
 IsSPermutable(g,h)
 )
 then
 return fail;
 fi;
 if IsNormal(g,h) or
 IsSPermutable(g,h)
 then
 return fail;
 fi;

 if IsSubnormal(g,h) then
 #
 # h cannot be S-permutable in g
 #
 return g;
 fi;
 bool2:=IsSubgroup(g,Parent(h));
 if bool2 then
 if
 (HasOneSubgroupInWhichSubnormalNotPermutableInParent(h)
 and OneSubgroupInWhichSubnormalNotPermutableInParent(h)<>fail)
 then
 return OneSubgroupInWhichSubnormalNotPermutableInParent(h);
 elif
 (HasOneSubgroupInWhichSubnormalNotSPermutableInParent(h)
 and OneSubgroupInWhichSubnormalNotSPermutableInParent(h)<>fail)
 then
 return OneSubgroupInWhichSubnormalNotSPermutableInParent(h);
 fi;
 fi;
 int:=IntermediateSubgroups(g,h);
 cex:=First(int.subgroups, t->not IsNormal(t,h) and IsSubnormal(t,h));
 if bool1 and bool2 then
 if cex=fail
 then
 SetIsWithSSubpermutizerConditionInParent(h,true);
 else
 SetIsWithSSubpermutizerConditionInParent(h,false);
 SetIsWithSubpermutizerConditionInParent(h,false);
 SetIsWithSubnormalizerConditionInParent(h,false);

 fi;
 fi;
 return cex;

end
 );

#############################################################################
##
#M IsWithSSubpermutizerCondition( <G>, <H> ) . . . . for groups
##
##
## This operation returns true if H satisfies the S-subpermutiser
## condition in G, otherwise it returns false.
## H satisfies the S-subpermutiser condition in G when H subnormal in K
## implies that H is S-permutable in K.
##

InstallMethod(IsWithSSubpermutizerConditionOp, "for finite groups",
 [IsGroup and IsFinite, IsGroup and IsFinite],
 function(g,h)
 local bool1,bool2;
 if not IsSubgroup(g,h)
 then
 Error("<h> must be a subgroup of <g>");
 fi;

 bool1:=IsSubgroup(Parent(h),g);
 if bool1 and
 (
 (HasOneSubgroupInWhichSubnormalNotNormalInParent(h) and
 OneSubgroupInWhichSubnormalNotNormalInParent(h)=fail)
 or
 (HasIsWithSubnormalizerConditionInParent(h) and
 IsWithSubnormalizerConditionInParent(h))
 or
 (HasOneSubgroupInWhichSubnormalNotPermutableInParent(h) and
 OneSubgroupInWhichSubnormalNotPermutableInParent(h)=fail)
 or
 (HasIsWithSubpermutizerConditionInParent(h) and
 IsWithSubpermutizerConditionInParent(h))
 or
 (HasOneSubgroupInWhichSubnormalNotSPermutableInParent(h) and
 OneSubgroupInWhichSubnormalNotSPermutableInParent(h)=fail)
 or
 (HasIsWithSSubpermutizerConditionInParent(h) and
 IsWithSSubpermutizerConditionInParent(h))
 )
 then
 return true;
 fi;
 bool2:=IsSubgroup(g,Parent(h));
 if bool2 and
 (
 (HasIsWithSSubpermutizerConditionInParent(h) and
 not IsWithSSubpermutizerConditionInParent(h))
 or
 (HasOneSubgroupInWhichSubnormalNotSPermutableInParent(h) and
 not OneSubgroupInWhichSubnormalNotSPermutableInParent(h)<>fail)
 )
 then
 return false;
 fi;
 return OneSubgroupInWhichSubnormalNotSPermutable(g,h)=fail;
end
 );

#############################################################################
##
#M AreMutuallyPermutableSubgroups( <G>, , <V> ) . . . . for finite groups
#M AreMutuallyPermutableSubgroups( , <V> )
##
## This operation returns true if and <V> are mutually permutable,
## otherwise it returns false.
## Two subgroups and <V> are mutually permutable
## if permutes with all subgroups of <V>
## and <V> permutes with all subgroups of .
##

InstallMethod(AreMutuallyPermutableSubgroups, "with three arguments",
 [IsGroup and IsFinite, IsGroup and IsFinite, IsGroup and IsFinite],
 function(G, A, B)
 local t;
 if not (IsSubgroup(G,A) and IsSubgroup(G,B))
 then
 Error("<A> and must be subgroups of <G>");
 fi;

 if not ArePermutableSubgroups(G,A,B)
 then
 return false;
 else
 if IsNormal(G,A) and IsNormal(G,B)
 then
 return true;
 fi;
 return (IsNormal(G,B) or
 ForAll(Zuppos(A),
 t->ArePermutableSubgroups(G,Subgroup(G,[t]),B)))
 and
 (IsNormal(G,A) or
 ForAll(Zuppos(B),
 t->ArePermutableSubgroups(G,A,Subgroup(G,[t]))));
 fi;
end
 );

InstallOtherMethod(AreMutuallyPermutableSubgroups, "with two arguments",
 [IsGroup and IsFinite, IsGroup and IsFinite],
 function(A, B)
 local t,G;
 if not ArePermutableSubgroups(A,B)
 then
 return false;
 else
 if IsIdenticalObj(Parent(A),Parent(B))
 then
 G:=Parent(A);
 else
 G:=ClosureGroup(A,B);
 fi;
 if IsNormal(G,A) and IsNormal(G,B)
 then
 return true;
 fi;
 return (IsNormal(G,B) or
 ForAll(Zuppos(A),
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