Ensure IsomorphismPermGroup returns an isomorphism

... for its argument.
gap-system · Jan 24, 2023 · 0c10e64 · 0c10e64
1 parent 3b361c1
commit 0c10e64
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Showing 2 changed files with 8 additions and 4 deletions.
diff --git a/lib/grpmat.gi b/lib/grpmat.gi
@@ -556,19 +556,18 @@ function(G)
 local map;
   if HasNiceMonomorphism(G) and IsPermGroup(Range(NiceMonomorphism(G))) then
     map:=NiceMonomorphism(G);
-    if IsIdenticalObj(Source(map),G) then
-      return map;
-    fi;
-    return GeneralRestrictedMapping(map,G,NiceObject(G));
   else
     if not HasIsFinite(G) then
       Info(InfoWarning,1,
            "IsomorphismPermGroup: The group is not known to be finite");
     fi;
     map:=NicomorphismOfGeneralMatrixGroup(G,false,false);
     SetNiceMonomorphism(G,map);
+  fi;
+  if IsIdenticalObj(Source(map),G) then
     return map;
   fi;
+  return GeneralRestrictedMapping(map,G,NiceObject(G));
 end);
 
 InstallMethod( IsomorphismPermGroup,

diff --git a/tst/testbugfix/2023-01-24-IsomorphismPermGroup.tst b/tst/testbugfix/2023-01-24-IsomorphismPermGroup.tst
@@ -0,0 +1,5 @@
+# see <https://github.com/gap-system/gap/issues/3601>
+gap> G:=SL(2,3);;Order(G);
+24
+gap> P:=Image(IsomorphismPermGroup(G));;Order(P);
+24