LOCAL
     the_reverse : oriented_edge;
   END_LOCAL;

   IF ('TOPOLOGY_SCHEMA.ORIENTED_EDGE' IN TYPEOF (an_edge) ) THEN
     the_reverse  := dummy_tri ||
             edge(an_edge.edge_end, an_edge.edge_start) ||
             oriented_edge(an_edge\oriented_edge.edge_element,
                        NOT (an_edge\oriented_edge.orientation)) ;
   ELSE
     the_reverse := dummy_tri ||
             edge(an_edge.edge_end, an_edge.edge_start) ||
             oriented_edge(an_edge, FALSE);
   END_IF;
   RETURN (the_reverse);