From: Andrea Asperti <andrea.asperti@unibo.it>
Date: Wed, 3 Jun 2009 14:42:12 +0000 (+0000)
Subject: not_to_not
X-Git-Tag: make_still_working~3929
X-Git-Url: http://matita.cs.unibo.it/gitweb/?a=commitdiff_plain;h=5dedda34c5f7b80d10bff717c5e6f90d0b92a5c7;p=helm.git

not_to_not
---

diff --git a/helm/software/matita/library/logic/connectives.ma b/helm/software/matita/library/logic/connectives.ma
index fcd046277..76d032316 100644
--- a/helm/software/matita/library/logic/connectives.ma
+++ b/helm/software/matita/library/logic/connectives.ma
@@ -32,6 +32,12 @@ qed.
 
 default "absurd" cic:/matita/logic/connectives/absurd.con.
 
+theorem not_to_not : \forall A,B:Prop. (A → B) \to ¬B →¬A.
+intros.unfold.intro.apply H1.apply (H H2).
+qed.
+
+default "absurd" cic:/matita/logic/connectives/absurd.con.
+
 inductive And (A,B:Prop) : Prop \def
     conj : A \to B \to (And A B).