+
+lemma orb_false_false :
+ ∀b1,b2:bool.((or_bool b1 b2) = false) → b1 = false.
+ intros 2;
+ elim b1 0;
+ elim b2;
+ simplify in H;
+ try destruct H;
+ reflexivity.
+qed.
+
+lemma orb_false_false_r :
+ ∀b1,b2:bool.((or_bool b1 b2) = false) → b2 = false.
+ intros 2;
+ elim b1 0;
+ elim b2;
+ simplify in H;
+ try destruct H;
+ reflexivity.
+qed.
+