proposition: Lemma setIDA A B C : A :&: (B :\: C) = (A :&: B) :\: C.
proof: Proof. by rewrite !setDE setIA. Qed.
imports: HB(structures) mathcomp(ssreflect ssrbool ssrfun eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop)