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diff --git a/matita/matita/contribs/lambdadelta/basic_2/syntax/ceq_ext_ceq_ext.ma b/matita/matita/contribs/lambdadelta/basic_2/syntax/ceq_ext_ceq_ext.ma
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+(**************************************************************************)
+(*       ___                                                              *)
+(*      ||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-.