proposition: Fact meetKU y x : join x (meet x y) = x.
proof: Proof. by elim: x y => [|? ? ih] [|? ?] //=; rewrite meetKU ih. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)