proposition: Fact meetKU y x : join x (meet x y) = x.
proof: Proof. by apply: eq_from_tnth => i; rewrite tnth_join tnth_meet meetKU. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)