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authorherbelin2003-11-07 22:19:14 +0000
committerherbelin2003-11-07 22:19:14 +0000
commitd35cb0f46fff92db0c44243f31beef4e29e2209f (patch)
treeab1dca2e920d1569f282dc08c571c8309a6dc4cf
parent646458624c8b858cef6227d890ee78faf96b6371 (diff)
Biblio standard sans impredicativite
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-(****************************************************************************)
-(* The Calculus of Inductive Constructions *)
-(* *)
-(* Projet LogiCal *)
-(* *)
-(* INRIA LRI-CNRS *)
-(* Rocquencourt Orsay *)
-(* *)
-(* May 29th 2002 *)
-(* *)
-(****************************************************************************)
-(* Hurkens_set.v *)
-(****************************************************************************)
-
-(*i logic: "-strongly-constructive" i*)
-
-(** This is Hurkens paradox [Hurkens] in system U-, adapted by Herman
- Geuvers [Geuvers] to show the inconsistency in the pure calculus of
- constructions of a retract from Prop into a small type. This file
- focus on the case of a retract into a small type in impredicative
- Set. As a consequence, Excluded Middle in Set is inconsistent with
- the impredicativity of Set.
-
-
- References:
-
- - [Hurkens] A. J. Hurkens, "A simplification of Girard's paradox",
- Proceedings of the 2nd international conference Typed Lambda-Calculi
- and Applications (TLCA'95), 1995.
-
- - [Geuvers] "Inconsistency of Classical Logic in Type Theory", 2001
- (see www.cs.kun.nl/~herman/note.ps.gz).
-*)
-
-(** We show that Hurkens paradox still hold for a retract from the
- negative fragment of Prop only, into bool:Set *)
-
-Section Hurkens_set_neg.
-
-Variable p2b : Prop -> bool.
-Variable b2p : bool -> Prop.
-Definition dn [A:Prop] := (A->False)->False.
-Hypothesis p2p1 : (A:Prop)(dn (b2p (p2b A)))->(dn A).
-Hypothesis p2p2 : (A:Prop)A->(b2p (p2b A)).
-
-Definition V := (A:Set)((A->bool)->(A->bool))->(A->bool).
-Definition U := V->bool.
-Definition sb : V -> V := [z][A;r;a](r (z A r) a).
-Definition le : (U->bool)->(U->bool) := [i][x](x [A;r;a](i [v](sb v A r a))).
-Definition induct: (U->bool)->Prop := [i](x:U)(b2p (le i x))->(dn (b2p (i x))).
-Definition WF : U := [z](p2b (induct (z U le))).
-Definition I : U->Prop :=
- [x]((i:U->bool)(b2p (le i x))->(dn (b2p (i [v](sb v U le x)))))->False.
-
-Lemma Omega : (i:U->bool)(induct i)->(dn (b2p (i WF))).
-Intros i y.
-Apply y.
-Unfold le WF induct.
-Apply p2p2.
-Intros x H0.
-Apply y.
-Exact H0.
-Qed.
-
-Lemma lemma : (induct [u](p2b (I u))).
-Unfold induct.
-Intros x p.
-Intro H; Apply H.
-Apply (p2p2 (I x)).
-Intro q.
-Apply (p2p1 (I [v:V](sb v U le x)) (q [u](p2b (I u)) p)).
-Intro H'; Apply H'.
-Intro i.
-Apply q with i:=[y:?](i [v:V](sb v U le y)).
-Qed.
-
-Lemma lemma2 : ((i:U->bool)(induct i)->(dn (b2p (i WF))))->False.
-Intro x.
-Apply (p2p1 (I WF) (x [u](p2b (I u)) lemma)).
-Intro H; Apply H.
-Intros i H0.
-Apply (x [y](i [v](sb v U le y))).
-Assert H1 : (dn (induct [y:U](i [v:V](sb v U le y)))).
-Assert H0' : (dn (b2p (le i WF))).
- Intro H1; Apply H1; Exact H0.
-Apply (p2p1 ? H0').
-Intros y H2 H3.
-Apply H1.
-Intro H4.
-Unfold induct in H4.
-Unfold dn in H4.
-Apply (H4 y H2 H3).
-Qed.
-
-Theorem Hurkens_set_neg : False.
-Exact (lemma2 Omega).
-Qed.
-
-End Hurkens_set_neg.
-
-Section EM_set_neg_inconsistency.
-
-Variable EM_set_neg : (A:Prop){~A}+{~~A}.
-
-Definition p2b [A:Prop] := if (EM_set_neg A) then [_]false else [_]true.
-Definition b2p [b:bool] := b=true.
-
-Lemma p2p1 : (A:Prop)~~(b2p (p2b A))->~~A.
-Proof.
-Intro A.
-Unfold p2b.
-NewDestruct (EM_set_neg A) as [_|Ha].
- Unfold b2p; Intros H Hna; Apply H; Discriminate.
- Tauto.
-Qed.
-
-Lemma p2p2 : (A:Prop)A->(b2p (p2b A)).
-Proof.
-Intro A.
-Unfold p2b.
-NewDestruct (EM_set_neg A) as [Hna|_].
- Intro Ha; Elim (Hna Ha).
- Intro; Unfold b2p; Reflexivity.
-Qed.
-
-Theorem not_EM_set_neg : False.
-Proof.
-Apply Hurkens_set_neg with p2b b2p.
-Apply p2p1.
-Apply p2p2.
-Qed.
-
-End EM_set_neg_inconsistency.
-
-Section EM_set_inconsistency.
-
-Variable EM_set_neg : (A:Prop){A}+{~A}.
-
-Theorem not_EM_set : False.
-Proof.
-Apply not_EM_set_neg.
-Intro A; Apply EM_set_neg.
-Qed.
-
-End EM_set_inconsistency.
-