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Fix a bug in SubgroupsSolvableGroups that could lead to wrong results #6802

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Fix a bug in SubgroupsSolvableGroups that could lead to wrong results #6802

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3 changes: 2 additions & 1 deletion lib/grppclat.gi
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Original file line number Diff line number Diff line change
Expand Up @@ -1034,7 +1034,8 @@ Assert(1,ForAll(bs,i->ForAll(efunc,j->Image(j,i)=i)));
l:=z.cocycleToComplement(com[kp]);
# the projection on the complement
k:=ClosureSubgroup(b,l);
if Length(s)=1 and IsOne(s[1]) then
if Length(s)=1 and IsOne(s[1])
and Dimension(z.oneCoboundaries)=0 then
# special case -- no conjugates
if ForAll(efunc,x->ForAll(GeneratorsOfGroup(l),
y->ImagesRepresentative(x,y) in k)) then
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5 changes: 5 additions & 0 deletions tst/testbugfix/2026-11-05-SubgroupsSolvableGroup.tst
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@@ -0,0 +1,5 @@
# Regression test for bug reported by H. Dietrich on 10/28/2026
gap> G := SmallGroup(12, 3);;
gap> a:=GroupHomomorphismByImages(G,G,[G.1,G.2,G.3],[G.1^2*G.2,G.3,G.2]);;
gap> Set(List(SubgroupsSolvableGroup(G, rec(actions := [a])), Size));
[ 1, 2, 3, 4, 12 ]
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