proposition: Lemma leEjoin x y : (x <= y) = (x `|` y == y).
proof: Proof. by rewrite leEmeet; apply/eqP/eqP => <-; rewrite (joinKI, meetUK). Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)