proposition: Lemma tnth_map f t i : tnth [tuple of map f t] i = f (tnth t i) :> rT.
proof: Proof. by apply: nth_map; rewrite size_tuple. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq choice fintype path)