FIX: (partial) for gap-system#2400

1) Wrong `IsTrivial` set in empty submagma 2) Fix `Submagma` method by replacing the empty submagma with the one-submagma, if it turns out a group. (Work around bug, not a fix)
hulpke · Apr 30, 2018 · 79f4e40 · 79f4e40
1 parent 3d5fd9f
commit 79f4e40
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Showing 2 changed files with 4 additions and 1 deletion.
diff --git a/lib/addmagma.gi b/lib/addmagma.gi
@@ -175,7 +175,7 @@ InstallGlobalFunction( SubadditiveMagmaNC, function( M, gens )
     if IsEmpty( gens ) then
       K:= NewType( FamilyObj(M),
                        IsAdditiveMagma
-                   and IsTrivial
+                   and IsEmpty
                    and IsAttributeStoringRep );
       S:= Objectify( K, rec() );
       SetGeneratorsOfAdditiveMagma( S, [] );

diff --git a/lib/magma.gi b/lib/magma.gi
@@ -1238,6 +1238,9 @@ InstallMethod( AsMagma,
     D := AsSSortedList( D );
     L := ShallowCopy( D );
     M := Submagma( MagmaByGenerators( D ), [] );
+    if IsGroup(M) then
+      M:=Submagma(MagmaByGenerators(D),[One(ElementsFamily(FamilyObj(D)))]);
+    fi;
     SubtractSet( L, AsSSortedList( M ) );
     while not IsEmpty(L)  do
         M := ClosureMagmaDefault( M, L[1] );