proposition: Lemma meetxx x : x `&` x = x.
proof: Proof. by rewrite -[X in _ `&` X](meetKU x) joinKI. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)