Merge pull request #566 from hungaborhorvath/DirectFactorBug

Correct bug in DirectFactorsOfGroup
gap-system · Feb 1, 2016 · 8d2a6c7 · 8d2a6c7
2 parents 08d4294 + 81485cf
commit 8d2a6c7
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Showing 2 changed files with 7 additions and 4 deletions.
diff --git a/lib/grpnames.gi b/lib/grpnames.gi
@@ -310,7 +310,7 @@ InstallMethod(DirectFactorsOfGroup, "if normal subgroups are computed", true,
       GGd := CommutatorFactorGroup(G);
       # if GGd is not cyclic of prime power size then there are at least two
       # maximal subgroups
-      if IsTrivial(GGd) or (IsCyclic(GGd) and IsPrimePowerInt(Size(GGd)))
+      if (IsTrivial(GGd) or (IsCyclic(GGd) and IsPrimePowerInt(Size(GGd))))
         and Length(MaximalNormalSubgroups(G))= 1 then
         # size of MaximalNormalSubgroups is an upper bound to the number of
         # components
@@ -437,7 +437,7 @@ InstallMethod(DirectFactorsOfGroup, "generic method", true,
       GGd := CommutatorFactorGroup(G);
       # if GGd is not cyclic of prime power size then there are at least two
       # maximal subgroups
-      if IsTrivial(GGd) or (IsCyclic(GGd) and IsPrimePowerInt(Size(GGd)))
+      if (IsTrivial(GGd) or (IsCyclic(GGd) and IsPrimePowerInt(Size(GGd))))
         and Length(MaximalNormalSubgroups(G))= 1 then
         # size of MaximalNormalSubgroups is an upper bound to the number of
         # components

diff --git a/tst/testinstall/direct_factors.tst b/tst/testinstall/direct_factors.tst
@@ -102,11 +102,14 @@ gap> DirectFactorsOfGroup(SymmetricGroup(4));
 [ Sym( [ 1 .. 4 ] ) ]
 gap> DirectFactorsOfGroup(SymmetricGroup(5));
 [ Sym( [ 1 .. 5 ] ) ]
-gap> G := Group([ (4,8)(6,10), (4,6,10,8,12), (2,4,12)(6,10,8), (3,9)(4,6,10,8,12)(7,11), (3,5)(4,6,10,8,12)(9,11), (1,3,11,9,5)(4,6,10,8,12) ]);;
+gap> G := Group([ (6,7,8,9,10), (8,9,10), (1,2)(6,7), (1,2,3,4,5)(6,7,8,9,10) ]);;
 gap> DirectFactorsOfGroup(G)=[G];
 true
-gap> G := Group([ (4,8)(6,10), (4,6,10,8,12), (2,4,12)(6,10,8), (3,9)(4,6,10,8,12)(7,11), (3,5)(4,6,10,8,12)(9,11), (1,3,11,9,5)(4,6,10,8,12) ]);;
+gap> G := Group([ (6,7,8,9,10), (8,9,10), (1,2)(6,7), (1,2,3,4,5)(6,7,8,9,10) ]);;
 gap> NormalSubgroups(G);;
 gap> DirectFactorsOfGroup(G)=[G];
 true
+gap> G := Group([ (4,8)(6,10), (4,6,10,8,12), (2,4,12)(6,10,8), (3,9)(4,6,10,8,12)(7,11), (3,5)(4,6,10,8,12)(9,11), (1,3,11,9,5)(4,6,10,8,12) ]);;
+gap> DirectFactorsOfGroup(G)=[ Group([ (4,8)(6,10), (4,6)(10,12), (2,12,8)(4,6,10) ]), Group([ (1,7,9)(3,5,11), (3,9)(7,11), (3,11)(5,7) ]) ];
+true
 gap> STOP_TEST("direct_factors.tst", 10000);