const SNo : set prop const Empty : set axiom SNo_0: SNo Empty const add_SNo : set set set term + = add_SNo infix + 2281 2280 axiom add_SNo_0L: !x:set.SNo x -> Empty + x = x const SNoLt : set set prop term < = SNoLt infix < 2020 2020 const minus_SNo : set set term - = minus_SNo axiom add_SNo_minus_Lt2b: !x:set.!y:set.!z:set.SNo x -> SNo y -> SNo z -> (z + y) < x -> z < x + - y claim !x:set.!y:set.SNo x -> SNo y -> x < y -> Empty < y + - x