summaryrefslogtreecommitdiff
path: root/theories7/Logic/ClassicalDescription.v
diff options
context:
space:
mode:
Diffstat (limited to 'theories7/Logic/ClassicalDescription.v')
-rw-r--r--theories7/Logic/ClassicalDescription.v76
1 files changed, 0 insertions, 76 deletions
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.
-