Around 1986, Colin McLarty, Charles Wells, and I noticed that Scientific American had recently published a few articles on subjects mathematical and decided to try to write one on variable set theory, AKA topos theory. Unfortunately, that particular window at Sci Am quickly closed. Our article was turned down and we forgot about it. More recently, I decided it might be interesting, or at least amusing to throw it open to the categorical community. The result can be found at ftp://ftp.math.mcgill.ca/barr/pdffiles/vst.pdf Michael -- Every gun that is made, every warship launched, every rocket fired signifies, in the final sense, a theft from those who hunger and are not fed, those who are cold and are not clothed. -Dwight D. Eisenhower [For admin and other information see: http://www.mta.ca/~cat-dist/ ]