proposition: Lemma leUx x y z : (x `|` y <= z) = (x <= z) && (y <= z).
proof: Proof. exact: (@lexI _ L^d). Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)