proposition: Lemma eqEsubset A B : (A == B) = (A \subset B) && (B \subset A).
proof: Proof. by apply/eqP/subset_eqP=> /setP. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop)