(* Forward lemmas with length for local environments ************************)
(* Basic_2A1: uses: TC_lpx_sn_fwd_length *)
-lemma rexs_fwd_length: ∀R,L1,L2,T. L1 ⪤*[R, T] L2 → |L1| = |L2|.
+lemma rexs_fwd_length: ∀R,L1,L2,T. L1 ⪤*[R,T] L2 → |L1| = |L2|.
#R #L1 #L2 #T #H elim H -L2
[ #L2 #HL12 >(rex_fwd_length … HL12) -HL12 //
| #L #L2 #_ #HL2 #IHL1