--- /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_2A/grammar/tsts.ma".
+
+(* SAME TOP TERM STRUCTURE **************************************************)
+
+(* Main properties **********************************************************)
+
+(* Basic_1: was: iso_trans *)
+theorem tsts_trans: Transitive … tsts.
+#T1 #T * -T1 -T //
+#I #V1 #V #T1 #T #X #H
+elim (tsts_inv_pair1 … H) -H #V2 #T2 #H destruct //
+qed-.
+
+theorem tsts_canc_sn: ∀T,T1. T ≂ T1 → ∀T2. T ≂ T2 → T1 ≂ T2.
+/3 width=3 by tsts_trans, tsts_sym/ qed-.
+
+theorem tsts_canc_dx: ∀T1,T. T1 ≂ T → ∀T2. T2 ≂ T → T1 ≂ T2.
+/3 width=3 by tsts_trans, tsts_sym/ qed-.