--- /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/ceq_ext_ceq_ext.ma".
+include "basic_2/relocation/sex_sex.ma".
+
+(* SYNTACTIC EQUIVALENCE FOR SELECTED LOCAL ENVIRONMENTS ********************)
+
+(* Main properties **********************************************************)
+
+theorem seq_trans: ∀f. Transitive … (seq f).
+/3 width=5 by sex_trans, ceq_ext_trans/ qed-.
+
+theorem seq_canc_sn: ∀f. left_cancellable … (seq f).
+/3 width=3 by sex_canc_sn, seq_trans, seq_sym/ qed-.
+
+theorem seq_canc_dx: ∀f. right_cancellable … (seq f).
+/3 width=3 by sex_canc_dx, seq_trans, seq_sym/ qed-.
+
+theorem seq_join: ∀f1,L1,L2. L1 ≡[f1] L2 → ∀f2. L1 ≡[f2] L2 →
+ ∀f. f1 ⋓ f2 ≘ f → L1 ≡[f] L2.
+/2 width=5 by sex_join/ qed-.
+
+theorem seq_meet: ∀f1,L1,L2. L1 ≡[f1] L2 → ∀f2. L1 ≡[f2] L2 →
+ ∀f. f1 ⋒ f2 ≘ f → L1 ≡[f] L2.
+/2 width=5 by sex_meet/ qed-.