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