const SNoLe : set set prop term <= = SNoLe infix <= 2020 2020 const Empty : set const abs_SNo : set set axiom nonneg_abs_SNo: !x:set.Empty <= x -> abs_SNo x = x const SNoLt : set set prop term < = SNoLt infix < 2020 2020 const SNo : set prop const minus_SNo : set set term - = minus_SNo var x:set hyp SNo x hyp x < Empty claim Empty <= - x -> abs_SNo - x = - x