proposition: Lemma leBKU y x : y <= x -> y `|` (x `\` y) = x.
proof: Proof. by move=> /join_r {2}<-; rewrite diffKU. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)