proposition: Lemma diffUK y x : (x `\` y) `|` y = x `|` y.
proof: Proof. by rewrite joinC diffKU joinC. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)