proposition: Lemma gt0_msetnP n x a : 0 < n -> reflect (x = a) (x \in msetn n a).
proof: Proof. by move=> n_gt0; rewrite inE n_gt0 /=; exact: eqP. Qed.
imports: mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop tuple) finmap