const SNoLt : set set prop term < = SNoLt infix < 2020 2020 const SNoLe : set set prop term <= = SNoLe infix <= 2020 2020 axiom SNoLtLe: !x:set.!y:set.x < y -> x <= y const Empty : set const abs_SNo : set set axiom nonneg_abs_SNo: !x:set.Empty <= x -> abs_SNo x = x claim !x:set.Empty < x -> abs_SNo x = x