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diff --git a/matita/matita/contribs/lambdadelta/ground_2/lib/bool.ma b/matita/matita/contribs/lambdadelta/ground_2/lib/bool.ma
index fed25ceda..d2acdb2bc 100644
--- a/matita/matita/contribs/lambdadelta/ground_2/lib/bool.ma
+++ b/matita/matita/contribs/lambdadelta/ground_2/lib/bool.ma
@@ -13,6 +13,7 @@
 (**************************************************************************)
 
 include "basics/bool.ma".
+include "ground_2/lib/star.ma".
 include "ground_2/notation/constructors/no_0.ma".
 include "ground_2/notation/constructors/yes_0.ma".
 
@@ -22,9 +23,16 @@ interpretation "boolean false" 'no = false.
 
 interpretation "boolean true" 'yes = true.
 
+(* Basic properties *********************************************************)
+
 lemma orb_false_r: ∀b1,b2:bool. (b1 ∨ b2) = false → b1 = false ∧ b2 = false.
 * normalize /2 width=1 by conj/ #b2 #H destruct
 qed-.
 
 lemma commutative_orb: commutative … orb.
 * * // qed.
+
+lemma eq_bool_dec: ∀b1,b2:bool. Decidable (b1 = b2).
+* * /2 width=1 by or_introl/
+@or_intror #H destruct
+qed-.