const SNo : set prop const add_SNo : set set set term + = add_SNo infix + 2281 2280 axiom SNo_add_SNo: !x:set.!y:set.SNo x -> SNo y -> SNo (x + y) claim !x:set.!y:set.!z:set.SNo x -> SNo y -> SNo z -> SNo (x + y + z)