proposition: Lemma joinUKI y x : meetU x (joinU x y) = x.
proof: Proof. by apply: val_inj; rewrite !SubK joinKI. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)