> Also, is it correct that the empty set is a subset of itself? Set theory was a long time ago, but one thing I remember is that every set has itself and the empty set as subsets of itself. In the case of the empty set these two are the same set (the empty set itself). --john -- John McDermott Writer, Educator, Consultant jjm@xxxxxxxxxx http://www.jkintl.com V +1 505/377-6293 F +1 505/377-6313