	/****** Reachable Nodes of a Graph (by Mauricio Osorio) ******/

mode none.
closure reach/1.

top(V) 	equals   reach({V}).

	reach(S)     contains S.
	reach({V\_}) contains reach(edges(V)).

	/* Directed Graph */

	edges(1) contains {2}. 
	edges(2) contains {3}.
	edges(3) contains {4}.
	edges(4) contains {1}.

