X-Git-Url: http://matita.cs.unibo.it/gitweb/?a=blobdiff_plain;f=helm%2Fsoftware%2Fmatita%2Flibrary%2Flogic%2Fconnectives.ma;h=76d0323166ad947578481e7c06bb4d8d8b3cc41a;hb=5dedda34c5f7b80d10bff717c5e6f90d0b92a5c7;hp=832d1a531fee7a18ee64c1de57997af27a867f15;hpb=916c558005ed665c62699a7a4c5347870c8a3efb;p=helm.git

diff --git a/helm/software/matita/library/logic/connectives.ma b/helm/software/matita/library/logic/connectives.ma
index 832d1a531..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).
 
@@ -69,7 +75,7 @@ definition decidable : Prop \to Prop \def \lambda A:Prop. A \lor \lnot A.
 inductive ex (A:Type) (P:A \to Prop) : Prop \def
     ex_intro: \forall x:A. P x \to ex A P.
 
-interpretation "exists" 'exists \eta.x = (ex _ x).
+interpretation "exists" 'exists x = (ex ? x).
 
 inductive ex2 (A:Type) (P,Q:A \to Prop) : Prop \def
     ex_intro2: \forall x:A. P x \to Q x \to ex2 A P Q.