proposition: Lemma widen_bseqK m n (lemn : m <= n) (lenm : n <= m) : cancel (@widen_bseq m n lemn) (widen_bseq lenm).
proof: Proof. by move=> t; apply: val_inj. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq choice fintype path)