Useful lemma added.

diff --git a/helm/matita/library/datatypes/bool.ma b/helm/matita/library/datatypes/bool.ma
index f4aec8167476b0d88204a06d3d23aaa798a323ac..3292e6789610f6114c590be58d18c729a3bf92fe 100644 (file)
--- a/helm/matita/library/datatypes/bool.ma
+++ b/helm/matita/library/datatypes/bool.ma
@@ -62,15 +62,21 @@ definition andb : bool \to bool \to bool\def
  [ true \Rightarrow b2
  | false \Rightarrow false ].
 
+(*CSC: the URI must disappear: there is a bug now *)
+interpretation "boolean and" 'and x y = (cic:/matita/datatypes/bool/andb.con x y).
+
 theorem andb_elim: \forall b1,b2:bool. \forall P:bool \to Prop.
 match b1 with
 [ true \Rightarrow P b2
-| false \Rightarrow P false] \to P (andb b1 b2).
+| false \Rightarrow P false] \to P (b1 \land b2).
 intros 3.elim b1.exact H. exact H.
 qed.
 
-(*CSC: the URI must disappear: there is a bug now *)
-interpretation "boolean and" 'and x y = (cic:/matita/datatypes/bool/andb.con x y).
+theorem andb_true_true: \forall b1,b2. (b1 \land b2) = true \to b1 = true.
+intro. elim b1.
+reflexivity.
+assumption.
+qed.
 
 definition orb : bool \to bool \to bool\def
 \lambda b1,b2:bool.