(* Basic forward lemmas *****************************************************)
-lemma leq_fwd_length: ∀L1,L2,d,e. L1 ≃[d, e] L2 → |L2| = |L1|.
+lemma leq_fwd_length: ∀L1,L2,d,e. L1 ≃[d, e] L2 → |L1| = |L2|.
#L1 #L2 #d #e #H elim H -L1 -L2 -d -e normalize //
qed-.