--- /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/grammar/lenv_length.ma".
+include "basic_2/relocation/lexs.ma".
+
+(* GENERAL ENTRYWISE EXTENSION OF A CONTEXT-SENSITIVE REALTION FOR TERMS ****)
+
+(* Forward lemmas on length for local environments **************************)
+
+(* Basic_2A1: includes: lpx_sn_fwd_length *)
+lemma lexs_fwd_length: ∀R,L1,L2,f. L1 ⦻*[R, f] L2 → |L1| = |L2|.
+#R #L1 #L2 #f #H elim H -L1 -L2 -f //
+qed-.