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 SNoLev : set set axiom ordinal_SNoLev: !x:set.ordinal x -> SNoLev x = x const SNo : set prop 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 -> SNoLev x = x -> y < x var x:set var y:set hyp ordinal x hyp SNo y hyp SNoLev y iIn x claim SNo x -> y < x