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+(************************************************************************)
+(* * The Coq Proof Assistant / The Coq Development Team *)
+(* v * INRIA, CNRS and contributors - Copyright 1999-2018 *)
+(* <O___,, * (see CREDITS file for the list of authors) *)
+(* \VV/ **************************************************************)
+(* // * This file is distributed under the terms of the *)
+(* * GNU Lesser General Public License Version 2.1 *)
+(* * (see LICENSE file for the text of the license) *)
+(************************************************************************)
+
+(** This module states propositional extensionality and draws
+ consequences of it *)
+
+Axiom propositional_extensionality :
+ forall (P Q : Prop), (P <-> Q) -> P = Q.
+
+Require Import ClassicalFacts.
+
+Theorem proof_irrelevance : forall (P:Prop) (p1 p2:P), p1 = p2.
+Proof.
+ apply ext_prop_dep_proof_irrel_cic.
+ exact propositional_extensionality.
+Qed.
+