const In : set set prop term iIn = In infix iIn 2000 2000 term Subq = \x:set.\y:set.!z:set.z iIn x -> z iIn y const ordinal : set prop const SNo : set prop axiom ordinal_SNo: !x:set.ordinal x -> SNo x const SNoR : set set const Empty : set lemma !x:set.ordinal x -> SNo x -> SNoR x = Empty claim !x:set.ordinal x -> SNoR x = Empty