proposition: Lemma lexU2 x y z : (x <= y) || (x <= z) -> x <= y `|` z.
proof: Proof. exact: (@leIx2 _ 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)