Fix EpimorphismSchurCover with two arguments for p-groups

gap-system · Sep 2, 2023 · 6c29511 · 6c29511
1 parent 597ea1a
commit 6c29511
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Showing 2 changed files with 25 additions and 3 deletions.
diff --git 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
@@ -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