proposition: Fact meetKU y x : join x (meet x y) = x.
proof: Proof. rewrite /meet /join /min /max !(fun_if, if_arg). by have []// := ltgtP x y; rewrite ltxx. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat choice seq) mathcomp(path fintype tuple bigop finset div prime finfun) mathcomp(finset)