proposition: Lemma memt_nth x0 (t : n.-tuple T) i : i < n -> nth x0 t i \in t.
proof: Proof. by move=> i_lt_n; rewrite mem_nth ?size_tuple. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq choice fintype path)