(* Contribution to the Coq Library   V6.3 (July 1999)                       *)
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(*                 The Calculus of Inductive Constructions                  *)
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(*                                Projet Coq                                *)
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(*                     INRIA                        ENS-CNRS                *)
(*              Rocquencourt                        Lyon                    *)
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(*                                Coq V5.11                                 *)
(*                              Feb 2nd 1996                                *)
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(*                (notations and layout updated March 2009)                 *)
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(*                            Setminus_fact.v                               *)
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(* This file is distributed under the terms of the                          *)
(* GNU Lesser General Public License Version 2.1                            *)
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Section Contravariance_of_Setminus.
Variable U : Type.

Lemma Setminus_contravariant :
forall A B B' : Ensemble U,
Included U B' B -> Included U (Setminus U A B) (Setminus U A B').