const SNo : set prop const add_SNo : set set set term + = add_SNo infix + 2281 2280 axiom SNo_add_SNo: !x:set.!y:set.SNo x -> SNo y -> SNo (x + y) const SNoLe : set set prop term <= = SNoLe infix <= 2020 2020 const abs_SNo : set set lemma !x:set.!y:set.SNo x -> SNo y -> SNo (x + y) -> abs_SNo (x + y) <= abs_SNo x + abs_SNo y claim !x:set.!y:set.SNo x -> SNo y -> abs_SNo (x + y) <= abs_SNo x + abs_SNo y