From 6c29511c3306b10e046364439e23675487324bd9 Mon Sep 17 00:00:00 2001 From: Max Horn Date: Fri, 1 Sep 2023 13:35:01 +0200 Subject: [PATCH] Fix `EpimorphismSchurCover` with two arguments for p-groups --- lib/schur.gi | 4 +--- .../2023-09-01-EpimorphismSchurCover.tst | 24 +++++++++++++++++++ 2 files changed, 25 insertions(+), 3 deletions(-) create mode 100644 tst/testbugfix/2023-09-01-EpimorphismSchurCover.tst diff --git a/lib/schur.gi b/lib/schur.gi index 0a511d7b33..7191e5f105 100644 --- a/lib/schur.gi +++ b/lib/schur.gi @@ -618,10 +618,8 @@ local G,pl; 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 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 diff --git a/tst/testbugfix/2023-09-01-EpimorphismSchurCover.tst b/tst/testbugfix/2023-09-01-EpimorphismSchurCover.tst new file mode 100644 index 0000000000..e4919325d2 --- /dev/null +++ b/tst/testbugfix/2023-09-01-EpimorphismSchurCover.tst @@ -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