proposition: Lemma joinBK x y : (y `|` x) `\` x = (y `\` x).
proof: Proof. by rewrite diffUx diffxx joinx0. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)