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