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Minor fixes that could go into 4.10 as well #3508

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Jun 25, 2019
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Minor fixes that could go into 4.10 as well #3508

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69726f4
ENHANCE: `EpimorphismSolvableQuotient` sets injective
hulpke May 6, 2019
5c69167
FIX: Wrong assumption about generators in radical factor
hulpke Jun 15, 2019
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3 changes: 1 addition & 2 deletions lib/grpcompl.gi
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Expand Up @@ -99,9 +99,8 @@ local G,N,K,s, h, q, fpi, factorpres, com, comgens, cen, ocrels, fpcgs, ncom,
Length(MappingGeneratorsImages(fpi)[2])," generators");
factorpres:=[FreeGeneratorsOfFpGroup(Range(fpi)),
RelatorsOfFpGroup(Range(fpi)),
List(MappingGeneratorsImages(fpi)[2],
List(GeneratorsOfGroup(Range(fpi)),
i->PreImagesRepresentative(fpi,i))];

Assert(1,ForAll(factorpres[3],i->Image(h,PreImagesRepresentative(h,i))=i));
# initialize
com:=[G];
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3 changes: 3 additions & 0 deletions lib/grppcfp.gi
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Expand Up @@ -878,6 +878,9 @@ local g, sq, hom;
g:=arg[1];
sq:=CallFuncList(SQ,arg);
hom:=GroupHomomorphismByImages(g,sq.image,GeneratorsOfGroup(g),sq.imgs);
if HasSize(g) and Size(g)=Size(sq.image) then
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if HasSize(g) and Size(g)=Size(sq.image) then
if HasSize(g) then

SetIsInjective(hom,true);
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SetIsInjective(hom,true);
SetIsInjective(hom, Size(g)=Size(sq.image));

fi;
return hom;
end);

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7 changes: 7 additions & 0 deletions tst/testbugfix/2019-04-09-Lattice.tst
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@@ -1,3 +1,10 @@
# see https://github.com/gap-system/gap/pull/3397
# and https://github.com/gap-system/gap/issues/3496
gap> l:=AllSmallGroups(960,IsSolvableGroup,false);;g:=l[5];;
gap> nat:=NaturalHomomorphismByNormalSubgroup(g,RadicalGroup(g));;
gap> fpi:=IsomorphismFpGroup(Group(GeneratorsOfGroup(Range(nat))));;
gap> fpi:=GroupHomomorphismByImages(Range(nat),Range(fpi),
> GeneratorsOfGroup(Range(nat)),List(GeneratorsOfGroup(Range(nat)),
> x->ImagesRepresentative(fpi,x)));;
gap> SetIsomorphismFpGroup(ImagesSource(nat),fpi);;
gap> StructureDescription(g);;t:=TableOfMarks(g);;