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diff --git a/theories7/Logic/ClassicalDescription.v b/theories7/Logic/ClassicalDescription.v deleted file mode 100644 index 85700c22..00000000 --- a/theories7/Logic/ClassicalDescription.v +++ /dev/null @@ -1,76 +0,0 @@ -(************************************************************************) -(* v * The Coq Proof Assistant / The Coq Development Team *) -(* <O___,, * CNRS-Ecole Polytechnique-INRIA Futurs-Universite Paris Sud *) -(* \VV/ **************************************************************) -(* // * This file is distributed under the terms of the *) -(* * GNU Lesser General Public License Version 2.1 *) -(************************************************************************) - -(*i $Id: ClassicalDescription.v,v 1.2.2.1 2004/07/16 19:31:29 herbelin Exp $ i*) - -(** This file provides classical logic and definite description *) - -(** Classical logic and definite description, as shown in [1], - implies the double-negation of excluded-middle in Set, hence it - implies a strongly classical world. Especially it conflicts with - impredicativity of Set, knowing that true<>false in Set. - - [1] Laurent Chicli, Loïc Pottier, Carlos Simpson, Mathematical - Quotients and Quotient Types in Coq, Proceedings of TYPES 2002, - Lecture Notes in Computer Science 2646, Springer Verlag. -*) - -Require Export Classical. - -Axiom dependent_description : - (A:Type;B:A->Type;R: (x:A)(B x)->Prop) - ((x:A)(EX y:(B x)|(R x y)/\ ((y':(B x))(R x y') -> y=y'))) - -> (EX f:(x:A)(B x) | (x:A)(R x (f x))). - -(** Principle of definite descriptions (aka axiom of unique choice) *) - -Theorem description : - (A:Type;B:Type;R: A->B->Prop) - ((x:A)(EX y:B|(R x y)/\ ((y':B)(R x y') -> y=y'))) - -> (EX f:A->B | (x:A)(R x (f x))). -Proof. -Intros A B. -Apply (dependent_description A [_]B). -Qed. - -(** The followig proof comes from [1] *) - -Theorem classic_set : (((P:Prop){P}+{~P}) -> False) -> False. -Proof. -Intro HnotEM. -Pose R:=[A,b]A/\true=b \/ ~A/\false=b. -Assert H:(EX f:Prop->bool|(A:Prop)(R A (f A))). -Apply description. -Intro A. -NewDestruct (classic A) as [Ha|Hnota]. - Exists true; Split. - Left; Split; [Assumption|Reflexivity]. - Intros y [[_ Hy]|[Hna _]]. - Assumption. - Contradiction. - Exists false; Split. - Right; Split; [Assumption|Reflexivity]. - Intros y [[Ha _]|[_ Hy]]. - Contradiction. - Assumption. -NewDestruct H as [f Hf]. -Apply HnotEM. -Intro P. -Assert HfP := (Hf P). -(* Elimination from Hf to Set is not allowed but from f to Set yes ! *) -NewDestruct (f P). - Left. - NewDestruct HfP as [[Ha _]|[_ Hfalse]]. - Assumption. - Discriminate. - Right. - NewDestruct HfP as [[_ Hfalse]|[Hna _]]. - Discriminate. - Assumption. -Qed. - |