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