--- /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 "static_2/syntax/ext2.ma".
+include "static_2/syntax/lenv.ma".
+
+(* EXTENSION TO BINDERS OF A CONTEXT-SENSITIVE RELATION FOR TERMS ***********)
+
+definition cext2: (lenv → relation term) → lenv → relation bind ≝
+ λR,L. ext2 (R L).
+
+(* Basic properties *********************************************************)
+
+lemma cext2_sym: ∀R. (∀L1,L2,T1,T2. R L1 T1 T2 → R L2 T2 T1) →
+ ∀L1,L2,I1,I2. cext2 R L1 I1 I2 → cext2 R L2 I2 I1.
+#R #HR #L1 #L2 #I1 #I2 * /3 width=2 by ext2_pair/
+qed-.
+
+lemma cext2_co: ∀R1,R2. (∀L,T1,T2. R1 L T1 T2 → R2 L T1 T2) →
+ ∀L,I1,I2. cext2 R1 L I1 I2 → cext2 R2 L I1 I2.
+#R1 #R2 #HR #L #I1 #I2 * /3 width=2 by ext2_unit, ext2_pair/
+qed-.