--- /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/relocation/sex_length.ma".
+include "basic_2/relocation/seq.ma".
+
+(* SYNTACTIC EQUIVALENCE FOR SELECTED LOCAL ENVIRONMENTS ********************)
+
+(* Forward lemmas with length for local environments ************************)
+
+(* Basic_2A1: includes: lreq_fwd_length *)
+lemma seq_fwd_length: ∀f,L1,L2. L1 ≡[f] L2 → |L1| = |L2|.
+/2 width=4 by sex_fwd_length/ qed-.