--- /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/lenv_ceq.ma".
+
+(* CONTEXT-DEPENDENT SYNTACTIC EQUIVALENCE FOR BINDERS **********************)
+
+(* Main properties **********************************************************)
+
+theorem ceq_ext_trans: ∀L1,I1,I. ceq_ext L1 I1 I →
+ ∀L2,I2. ceq_ext L2 I I2 → ∀L3. ceq_ext L3 I1 I2.
+#L1 #I1 #I * -I1 -I //
+#I1 #V1 #V #HV1 #L2 #Z #H elim (ext2_inv_pair_sn … H) -H //
+qed-.