--- /dev/null
+(**************************************************************************)
+(* ___ *)
+(* ||M|| *)
+(* ||A|| A project by Andrea Asperti *)
+(* ||T|| *)
+(* ||I|| Developers: *)
+(* ||T|| The HELM team. *)
+(* ||A|| http://helm.cs.unibo.it *)
+(* \ / *)
+(* \ / This file is distributed under the terms of the *)
+(* v GNU General Public License Version 2 *)
+(* *)
+(**************************************************************************)
+
+include "basic_2/syntax/term.ma".
+
+(* BINDERS FOR LOCAL ENVIRONMENTS ******************************************)
+
+inductive bind: Type[0] ≝
+| BUnit: bind1 → bind
+| BPair: bind2 → term → bind
+.
+
+(* Basic properties ********************************************************)
+
+lemma eq_bind_dec: ∀I1,I2:bind. Decidable (I1 = I2).
+* #I1 [2: #V1 ] * #I2 [2,4: #V2 ]
+[ elim (eq_bind2_dec I1 I2) #HI
+ [ elim (eq_term_dec V1 V2) #HV /2 width=1 by or_introl/ ]
+ @or_intror #H destruct /2 width=1 by/
+| @or_intror #H destruct
+| @or_intror #H destruct
+| elim (eq_bind1_dec I1 I2) #HI /2 width=1 by or_introl/
+ @or_intror #H destruct /2 width=1 by/
+]
+qed-.