(************************************************************************)
(*         *   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)         *)
(************************************************************************)
(* File created for Coq V5.10.14b, Oct 1995 *)
(* Classical tactics for proving disjunctions by Julien Narboux, Jul 2005 *)
(* Inferred proof-irrelevance and eq_rect_eq added by Hugo Herbelin, Mar 2006 *)
(** Classical Propositional Logic *)
Hint Unfold not: core.
(** Peirce's law states [forall P Q:Prop, ((P -> Q) -> P) -> P]. Thanks to [forall P, False -> P], it is equivalent to the following form *)

Lemma not_imply_elim2 : forall P Q:Prop, ~ (P -> Q) -> ~ Q.