const SNo : set prop const SNoLt : set set prop term < = SNoLt infix < 2020 2020 const minus_SNo : set set term - = minus_SNo axiom minus_SNo_Lt_contra: !x:set.!y:set.SNo x -> SNo y -> x < y -> - y < - x const SNoLe : set set prop term <= = SNoLe infix <= 2020 2020 axiom SNoLtLe: !x:set.!y:set.x < y -> x <= y axiom SNoLe_ref: !x:set.x <= x axiom SNoLeE: !x:set.!y:set.SNo x -> SNo y -> x <= y -> x < y | x = y claim !x:set.!y:set.SNo x -> SNo y -> x <= y -> - y <= - x