proposition: Lemma setCS A B : (~: A \subset ~: B) = (B \subset A).
proof: Proof. by rewrite !subsets_disjoint setCK disjoint_sym. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop)