const SNo : set prop const Empty : set axiom SNo_0: SNo Empty const minus_SNo : set set term - = minus_SNo axiom SNo_minus_SNo: !x:set.SNo x -> SNo - x const add_SNo : set set set term + = add_SNo infix + 2281 2280 axiom add_SNo_minus_SNo_rinv: !x:set.SNo x -> x + - x = Empty axiom add_SNo_0L: !x:set.SNo x -> Empty + x = x axiom add_SNo_cancel_L: !x:set.!y:set.!z:set.SNo x -> SNo y -> SNo z -> x + y = x + z -> y = z claim - Empty = Empty