diff --git a/library/ugraphs.yap b/library/ugraphs.yap
index ef128b937..f6e799b99 100644
--- a/library/ugraphs.yap
+++ b/library/ugraphs.yap
@@ -233,19 +233,19 @@ p_to_s_graph(P_Graph, S_Graph) :-
 	p_to_s_group(VertexSet, EdgeSet, S_Graph).
  
  
-p_to_s_vertices([], []) :- !.
+p_to_s_vertices([], []).
 p_to_s_vertices([A-Z|Edges], [A,Z|Vertices]) :-
 	p_to_s_vertices(Edges, Vertices).
  
  
-p_to_s_group([], _, []) :- !.
+p_to_s_group([], _, []).
 p_to_s_group([Vertex|Vertices], EdgeSet, [Vertex-Neibs|G]) :-
 	p_to_s_group(EdgeSet, Vertex, Neibs, RestEdges),
 	p_to_s_group(Vertices, RestEdges, G).
  
  
 p_to_s_group([V1-X|Edges], V2, [X|Neibs], RestEdges) :- V1 == V2, !,
-	p_to_s_group(Edges, V, Neibs, RestEdges).
+	p_to_s_group(Edges, V2, Neibs, RestEdges).
 p_to_s_group(Edges, _, [], Edges).