Determine whether this argument, taken from Kalish and Montague [KaMo64], is valid.
If Superman were able and willing to prevent evil,he would do so. If Superman were unable to prevent evil, he would be impotent; if he were unwilling to prevent evil, he would be malevolent. Superman does not prevent evil. If Superman exists, he is neither impotent nor malevolent. Therefore, Superman does not exist.