proposition: Lemma tagged_tuple_bseqK {n T} : cancel (@tagged_tuple_bseq n T) bseq_tagged_tuple.
proof: Proof. move=> [[k lt_kn] t]; apply: eq_existT_curried => [|k_eq]; apply/val_inj. by rewrite /= size_tuple. by refine (let: erefl := k_eq in _). Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq choice fintype path)