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(************************************************************************)
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(* v * The Coq Proof Assistant / The Coq Development Team *)
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(* <O___,, * CNRS-Ecole Polytechnique-INRIA Futurs-Universite Paris Sud *)
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(* \VV/ **************************************************************)
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(* // * This file is distributed under the terms of the *)
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(* * GNU Lesser General Public License Version 2.1 *)
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(************************************************************************)
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(*i $Id: Classical_Pred_Type.v 8642 2006-03-17 10:09:02Z notin $ i*)
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(** Classical Predicate Logic on Type *)
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Require Import Classical_Prop.
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(** de Morgan laws for quantifiers *)
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Lemma not_all_not_ex :
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forall P:U -> Prop, ~ (forall n:U, ~ P n) -> exists n : U, P n.
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apply abs; exists n; exact H.
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Lemma not_all_ex_not :
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forall P:U -> Prop, ~ (forall n:U, P n) -> exists n : U, ~ P n.
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apply not_all_not_ex with (P:=fun x => ~ P x).
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intro all; apply notall.
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Lemma not_ex_all_not :
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forall P:U -> Prop, ~ (exists n : U, P n) -> forall n:U, ~ P n.
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Proof. (* Intuitionistic *)
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unfold not in |- *; intros P notex n abs.
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Lemma not_ex_not_all :
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forall P:U -> Prop, ~ (exists n : U, ~ P n) -> forall n:U, P n.
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red in |- *; intro K; apply H; exists n; trivial.
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Lemma ex_not_not_all :
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forall P:U -> Prop, (exists n : U, ~ P n) -> ~ (forall n:U, P n).
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Proof. (* Intuitionistic *)
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unfold not in |- *; intros P exnot allP.
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Lemma all_not_not_ex :
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forall P:U -> Prop, (forall n:U, ~ P n) -> ~ (exists n : U, P n).
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Proof. (* Intuitionistic *)
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unfold not in |- *; intros P allnot exP; elim exP; intros n p.
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apply allnot with n; auto.