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 ordsucc : set set const SNoLe : set set prop term <= = SNoLe infix <= 2020 2020 lemma !x:set.!y:set.ordinal x -> ordinal y -> x iIn ordsucc y -> SNo x -> x <= y var x:set var y:set hyp ordinal x hyp ordinal y hyp Subq x y claim x iIn ordsucc y -> x <= y