const SNo : set prop 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_R2: !x:set.!y:set.SNo x -> SNo y -> (x + y) + - y = x axiom minus_SNo_invol: !x:set.SNo x -> - - x = x claim !x:set.!y:set.SNo x -> SNo y -> (x + - y) + y = x