proposition: Lemma disjoint_lexUr z x y : x `&` z = \bot -> (x <= z `|` y) = (x <= y).
proof: Proof. by move=> xz0; rewrite joinC; rewrite disjoint_lexUl. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)