proposition: Fact meetKU y x : join x (meet x y) = x.
proof: Proof. apply/le_anti/andP; split; last exact: join_leL. by rewrite joinP le_refl meet_leL. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)