proposition: Lemma le_def A B : A \subset B = (A :&: B == A).
proof: Proof. exact/setIidPl/eqP. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)