proposition: Lemma leBx x y : x `\` y <= x.
proof: Proof. by rewrite -{2}[x](joinIB y) lexU2 // lexx orbT. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)