proposition: Lemma diffBx x y z : (x `\` y) `\` z = x `\` (y `|` z).
proof: Proof. apply/eqP; rewrite eq_diff leBr ?leUl //=. by rewrite diffxU joinIr diffKU -joinIr meet_l ?leUr //= -meetA diffIK meetx0. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)