(* Basic_2A1: includes: lpx_sn_fwd_length *)
lemma lexs_fwd_length: ∀RN,RP,f,L1,L2. L1 ⪤*[RN, RP, f] L2 → |L1| = |L2|.
#RM #RP #f #L1 #L2 #H elim H -f -L1 -L2 //
-#f #I #L1 #L2 #V1 #V2 >length_pair >length_pair //
+#f #I1 #I2 #L1 #L2 >length_bind >length_bind //
qed-.