Re: Is {{}} a valid construct?

>> Can an empty set contain an empty set? Is it valid according to set theory? If so, what does it correlate to in the real world? (when last explained to me, I was left holding two empty bags of potatoes but no clear understanding :) <<

Look up "ordinal numbers" in a book on set theory. This is how they are defined and the work on this was due to John von Neumann -- the same guy that invented Game Theory and the basic architecture for stored programs in computers. The idea is that 0 = {} and then a + 1 = a U {a} to build integers with a version of Peano's system. Received on Sat Feb 03 2007 - 16:32:07 CET