const In : set set prop term iIn = In infix iIn 2000 2000 term nIn = \x:set.\y:set.~ x iIn y const ordinal : set prop const SNo : set prop axiom ordinal_SNo: !x:set.ordinal x -> SNo x const SNoLev : set set const SNoLt : set set prop term < = SNoLt infix < 2020 2020 lemma !x:set.!y:set.ordinal x -> SNo y -> SNoLev y iIn x -> SNo x -> y < x claim !x:set.ordinal x -> !y:set.SNo y -> SNoLev y iIn x -> y < x