(* Contribution to the Coq Library   V6.3 (July 1999)                    *)
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(* File: ZFbasis.v                                                         *)
(* auteur: alex@sysal.ibp.fr                                               *)
(* date: 19/10/95                                                          *)
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Require Export useful.
Parameter E : Set.
Parameter In : E -> E -> Prop. (* x \in y ==> In x y *)

Lemma lem_eq_or : forall a b c : E, a = c \/ b = c <-> c = a \/ c = b.
intros; unfold iff in |- *; split; intros.