X-Git-Url: http://matita.cs.unibo.it/gitweb/?a=blobdiff_plain;f=helm%2Fsoftware%2Fmatita%2Flibrary%2Flogic%2Fconnectives.ma;h=76d0323166ad947578481e7c06bb4d8d8b3cc41a;hb=dc74ed7c4af1aa9b90fc5d2f0a86bd7825696e71;hp=fcd046277fda5e50dfdd8bce702d065b14b789a1;hpb=e78cf74f8976cf0ca554f64baa9979d0423ee927;p=helm.git

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).