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Sep 17, 2014 at 15:13 comment added Lennart Meier It is a bit like: Assume there were no proofs by contradiction....
Jul 6, 2012 at 4:37 comment added Noam D. Elkies Assume there was no empty set. Consider the set of all empty sets, ... [seen years ago in Martin Gardner; not sure of the original source]
May 9, 2011 at 9:09 comment added Zsbán Ambrus I don't understand the distinction between the empty set and other sets here. If mathematicians construct sets from other sets, then they could construct the empty set from other sets as well.
May 8, 2011 at 22:03 history answered Michael Renardy CC BY-SA 3.0