#(C) Graham Ellis, 2005-2006

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InstallGlobalFunction(PrimePartDerivedFunctor,
function(G,R,F,n)
local
	C,P,P1, D,DCRS, L, AscChn,
	K, gensK, S, f,fx,
	HP, HK, HPK, HKhomHPK, HPKhomHP, HKhomHP,
	HKx,HPKx, 
	HKxhomHPKx, HPKxhomHP, HKxhomHP, HKhomHKx,  HKhomHP2,
	HPrels, x, y, i,prime,  
	HPpres,G1,newDCRS;

C:=F(R);

P:=R!.group;
prime:=PrimePGroup(P);
P1:=Normalizer(G,P);
AscChn:=AscendingChain(G,P1);
D:= List(DoubleCosetRepsAndSizes(P1,P,P), x->x[1]);
D:=List(SmallGeneratingSet(P1),x->x);
DCRS:=D;

for i in [2..Length(AscChn)] do
D:=List(DoubleCosetRepsAndSizes(AscChn[i],AscChn[i-1],AscChn[i-1]),
x->x[1]);
Append(DCRS,D);
newDCRS:=[];
for x in DCRS do
for y in D do
Add(newDCRS,y*x);
od;od;
DCRS:=SSortedList(newDCRS);
od;


HP:=GroupHomomorphismByFunction(P,P,x->x);
HP:=EquivariantChainMap(R,R,HP);
HP:=F(HP);
HP:=Homology(HP,n);
HP:=Source(HP);
if Length(AbelianInvariants(HP))=0 then return []; fi;

HPrels:=[Identity(HP)];

for L in DCRS do
K:=Intersection(P,P^L);

if Order(K)>1 then


gensK:=ReduceGenerators(GeneratorsOfGroup(K),K);

G1:=Group(Concatenation(gensK,[Identity(P)]));
if Order(G1)<=32 then
S:=ResolutionFiniteGroup(gensK,n+1);
else
S:=ResolutionNormalSeries(LowerCentralSeries(G1),n+1);
fi;

if Length(Homology(F(S),n))>0 then

f:=GroupHomomorphismByFunction(K,P,x->x);
HKhomHPK:=Homology(F(EquivariantChainMap(S,R,f)),n);
HK:=Source(HKhomHPK);

HPK:=Range(HKhomHPK);
HPKhomHP:=GroupHomomorphismByImagesNC(HPK,HP,GeneratorsOfGroup(HPK),
                                                  GeneratorsOfGroup(HP));
HKhomHP:=GroupHomomorphismByFunction(HK,HP,x->
Image(HPKhomHP, Image(HKhomHPK,x) ) );

fx:=GroupHomomorphismByFunction(K,P,g->Image(f,g)^(L^-1));
HKxhomHPKx:=Homology(F(EquivariantChainMap(S,R,fx)),n);
HKx:=Source(HKxhomHPKx);
HPKx:=Parent(Image(HKxhomHPKx));
HPKxhomHP:=GroupHomomorphismByImagesNC(HPKx,HP,GeneratorsOfGroup(HPKx),
                                                  GeneratorsOfGroup(HP));
HKxhomHP:=GroupHomomorphismByFunction(HKx,HP,x->
Image(HPKxhomHP, Image(HKxhomHPKx,x) ) );
HKhomHKx:=GroupHomomorphismByImagesNC(HK,HKx,GeneratorsOfGroup(HK),GeneratorsOfGroup(HKx));
HKhomHP2:=GroupHomomorphismByFunction(HK,HP,a->
Image(HKxhomHP, Image(HKhomHKx,a)));

for x in GeneratorsOfGroup(HK) do
Append(HPrels, [Image(HKhomHP,x)*Image(HKhomHP2,x)^-1]);
od;

fi;
fi;
od;

return AbelianInvariants(HP/NormalClosure(HP,Group(HPrels)));
end);
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