1 PROCEDURE (G: reduced graph)
 2 	Let S(v) be a set of successors of v
 3 	Let R be an empty set
 4
 5 	//assign integer labels sinks and isolated vertices.
 6 	FOR each v in G
 7     Find S(v) successors of v
 8     IF S(v) is assigned to layers
 9       Add v to R
10       Remove v from G
11     ENDIF
12 	END LOOP
13 END PROCEDURE