+ ∧∧ |L1|-|L2| = n1 & |L2|-|L1| = n2.
+#L1 #L2 #n1 #n2 #H elim H -L1 -L2 -n1 -n2 /2 width=1 by conj/
+#K1 #K2 #n #_ * #H1 #H2 >length_bind /3 width=1 by minus_Sn_m, conj/
+qed-.
+
+lemma lveq_inj_length: ∀L1,L2,n1,n2. L1 ≋ⓧ*[n1, n2] L2 →
+ |L1| = |L2| → ∧∧ 0 = n1 & 0 = n2.
+#L1 #L2 #n1 #n2 #H #HL
+elim (lveq_fwd_length … H) -H
+>HL -HL /2 width=1 by conj/
+qed-.
+
+lemma lveq_fwd_length_plus: ∀L1,L2,n1,n2. L1 ≋ⓧ*[n1, n2] L2 →
+ |L1| + n2 = |L2| + n1.