gprd: fix PrimePGroup for trivial direct products

gap-system · Oct 2, 2017 · 4a25b3c · 4a25b3c
1 parent 221df9d
commit 4a25b3c
Show file tree

Hide file tree

Showing 2 changed files with 21 additions and 2 deletions.
diff --git a/lib/gprd.gi b/lib/gprd.gi
@@ -263,10 +263,15 @@ end );
 InstallMethod( PrimePGroup, "for direct products",
  [IsPGroup and HasDirectProductInfo],
 function( D )
- local groups, p;
+ local groups, p, H;
  groups := DirectProductInfo(D).groups;
  Assert(1, ForAll(groups, IsPGroup));
- p := PrimePGroup(First(groups, G -> PrimePGroup(G) <> fail));
+ H := First(groups, G -> PrimePGroup(G) <> fail);
+ if H = fail then
+ SetIsTrivial(D, true);
+ return fail;
+ fi;
+ p := PrimePGroup(H);
  Assert(1, ForAll(groups, G -> PrimePGroup(G) in [fail, p]));
  return p;
 end );

diff --git a/tst/testbugfix/2017-09-29-PrimePGroup.tst b/tst/testbugfix/2017-09-29-PrimePGroup.tst
@@ -0,0 +1,14 @@
+# Issue related to PrimePGroup for a direct product of trivial groups
+#
+gap> G := DirectProduct(TrivialGroup(IsPcGroup), TrivialGroup(IsPcGroup));
+<pc group of size 1 with 0 generators>
+gap> PrimePGroup(G);
+fail
+gap> A := Group(Transformation([1, 2, 3]));;
+gap> B := DirectProduct(A, A);;
+gap> IsPGroup(B);
+true
+gap> HasDirectProductInfo(B);
+true
+gap> PrimePGroup(B);
+fail