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(* 02110-1301 USA                                                     *)
(* Contribution to the Coq Library   V6.3 (July 1999)                    *)
(* Just for fun : a proof that there is no set of all sets, using       *)
(* Russell's paradox construction                                       *)
(* There, of course, are other proofs (foundation, etc)                 *)

Theorem Russell : forall E : Ens, (forall E' : Ens, IN E' E) -> False.