proposition: Lemma tvalK n (t : n.-tuple T) : in_tuple t = tcast (esym (size_tuple t)) t.
proof: Proof. by apply: val_inj => /=; case: _ / (esym _). Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq choice fintype path)