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Fix EpimorphismSchurCover with two arguments for p-groups #5501

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4 changes: 1 addition & 3 deletions lib/schur.gi
Original file line number Diff line number Diff line change
Expand Up @@ -618,10 +618,8 @@
G:=arg[1];
if not IsFinite(G) then
Error("cover is only defined for finite groups");
elif Size(G)=1 then
elif IsTrivial(G) then

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return IdentityMapping(G);
elif IsPGroup(G) then
TryNextMethod(); # we recursively call the algorithm for the p-sylow
fi;
Info(InfoWarning,1,"Warning: EpimorphismSchurCover via Holt's algorithm is under construction");
if Length(arg)>1 then
Expand Down
24 changes: 24 additions & 0 deletions tst/testbugfix/2023-09-01-EpimorphismSchurCover.tst
Original file line number Diff line number Diff line change
@@ -0,0 +1,24 @@
#
gap> G:=SmallGroup(4,2);;
gap> epi:=EpimorphismSchurCover(G,[2]);;
#I Warning: EpimorphismSchurCover via Holt's algorithm is under construction
gap> Size(Kernel(epi));
2

#
gap> epi:=EpimorphismSchurCover(AlternatingGroup(5), [2,3,5,7]);;
#I Warning: EpimorphismSchurCover via Holt's algorithm is under construction
gap> Size(Kernel(epi));
2

#
gap> epi:=EpimorphismSchurCover(AlternatingGroup(5), [3,5,7]);;
#I Warning: EpimorphismSchurCover via Holt's algorithm is under construction
gap> Size(Kernel(epi));
1

#
gap> epi:=EpimorphismSchurCover(SylowSubgroup(AlternatingGroup(5),2), [2,3,5,7]);;
#I Warning: EpimorphismSchurCover via Holt's algorithm is under construction
gap> Size(Kernel(epi));
2