proposition: Lemma diffKU y x : y `|` (x `\` y) = y `|` x.
proof: Proof. apply/eqP; rewrite eq_le leU2 //= leUx leUl. by apply/meet_idPl; have := joinIB y x; rewrite joinIl join_l. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)