proposition: Lemma eqEmsubset A B : (A == B) = (A `<=` B) && (B `<=` A).
proof: Proof. apply/eqP/andP => [<-|[/msubsetP AB /msubsetP BA]]; first by split. by apply/msetP=> a; apply/eqP; rewrite eqn_leq AB BA. Qed.
imports: mathcomp(ssreflect ssrbool ssrnat eqtype ssrfun seq) mathcomp(choice path finset finfun fintype bigop tuple) finmap