proposition: Lemma joinIB y x : (x `&` y) `|` (x `\` y) = x.
proof: Proof. exact: joinIB. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)