Support AbelianInvariants for infinite cyclic groups

gap-system · Mar 17, 2023 · e97be8e · e97be8e
1 parent 577dcec
commit e97be8e
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diff --git a/lib/grp.gi b/lib/grp.gi
@@ -872,6 +872,9 @@ InstallMethod( AbelianInvariants,
     local   H,  p,  l,  r,  i,  j,  gns,  inv,  ranks, g,  cmm;
 
     if not IsFinite(G)  then
+        if HasIsCyclic(G) and IsCyclic(G) then
+          return [ 0 ];
+        fi;
         TryNextMethod();
     elif IsTrivial( G )  then
         return [];

diff --git a/tst/testinstall/opers/AbelianInvariants.tst b/tst/testinstall/opers/AbelianInvariants.tst
@@ -0,0 +1,10 @@
+gap> START_TEST("AbelianInvariants.tst");
+
+#
+gap> G := Group( [ [ [ 2, 1 ], [ 17, 8 ] ] ] );
+Group([ [ [ 2, 1 ], [ 17, 8 ] ] ])
+gap> AbelianInvariants(G);
+[ 0 ]
+
+#
+gap> STOP_TEST( "AbelianInvariants.tst", 1);