proposition: Lemma diff_eq0 x y : (x `\` y == \bot) = (x <= y).
proof: Proof. by rewrite -lex0 leBLR joinx0. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)