I just happened across this and thought some of you might like it. Includes some nice pictures and an interesting bit about symmetric gray codes. http://www.theory.csc.uvic.ca/~cos/venn/VennSymmEJC.html Found while browsing "The Geometry Junkyard" http://www.ics.uci.edu/~eppstein/junkyard/topic.html which has some other fun and odd stuff.