const Sep : set (set prop) set const Power : set set const Sigma : set (set set) set const Union : set set const In : set set prop term iIn = In infix iIn 2000 2000 const ap : set set set term Pi = \x:set.\f:set set.Sep (Power (Sigma x \y:set.Union (f y))) \y:set.!z:set.z iIn x -> ap y z iIn f z axiom SepE2: !x:set.!p:set prop.!y:set.y iIn Sep x p -> p y claim !x:set.!f:set set.!y:set.!z:set.y iIn Pi x f -> z iIn x -> ap y z iIn f z