proposition: Lemma cast_bseqKV m n (eq_mn : m = n) : cancel (cast_bseq (esym eq_mn)) (cast_bseq eq_mn).
proof: Proof. by case: n / eq_mn. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq choice fintype path)