X-Git-Url: http://matita.cs.unibo.it/gitweb/?a=blobdiff_plain;f=helm%2Fsoftware%2Fmatita%2Flibrary%2Flogic%2Fcprop_connectives.ma;h=c0bbdda18f3212715b49e5c8412cb7523c81e2ce;hb=b14d3611e67633ffa5b661e38331db4ea83ca429;hp=3b43ef3993670c4699354fd8417d37cda8e83025;hpb=c2bf3797d41b0fd06588f5c7d0fbd02d1219371d;p=helm.git

diff --git a/helm/software/matita/library/logic/cprop_connectives.ma b/helm/software/matita/library/logic/cprop_connectives.ma
index 3b43ef399..c0bbdda18 100644
--- a/helm/software/matita/library/logic/cprop_connectives.ma
+++ b/helm/software/matita/library/logic/cprop_connectives.ma
@@ -58,6 +58,13 @@ notation < "hvbox(a break ∧ b break ∧ c break ∧ d)" with precedence 35 for
  
 interpretation "constructive quaternary and" 'and4 x y z t = (And4 x y z t).
 
+record Iff (A,B:CProp) : CProp ≝
+ { if: A → B;
+   fi: B → A
+ }.
+
+interpretation "logical iff" 'iff x y = (Iff x y).
+
 inductive exT (A:Type) (P:A→CProp) : CProp ≝
   ex_introT: ∀w:A. P w → exT A P.