beginning proof of chebyshev's bound on prim.

[helm.git] / helm / software / matita / library / logic / connectives.ma

diff --git a/helm/software/matita/library/logic/connectives.ma b/helm/software/matita/library/logic/connectives.ma
index bb08b8038bf51c37d533a0889c2493fd04fdc810..5afc3e5dc29d7db0f45e812d244f6cd72e4ff7f6 100644 (file)
--- a/helm/software/matita/library/logic/connectives.ma
+++ b/helm/software/matita/library/logic/connectives.ma
@@ -82,3 +82,5 @@ interpretation "exists" 'exists \eta.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.
 
+definition iff :=
+ \lambda A,B. (A -> B) \land (B -> A).
\ No newline at end of file