Ali Baba Variant 

The cited Nalebuff article lists multiple possible answers to the apparent paradox.  The only one which implies either Ali or Baba should possibly want to trade is one in which there is a maximum apparent amount of money that might be in the envelope (Nalebuff, The Other Person's Envelope is Always Greener, 1989, pp. 175-177).209.6.139.197  David Lepzelter