const Sep : set (set prop) set const UnivOf : set set const Empty : set const nat_p : set prop term omega = Sep (UnivOf Empty) nat_p const In : set set prop term iIn = In infix iIn 2000 2000 axiom SepE2: !x:set.!p:set prop.!y:set.y iIn Sep x p -> p y claim !x:set.x iIn omega -> nat_p x