 The other solution to the fission problem abandons the intuitive claim that psychological continuity by itself suffices for us to persist. It says, rather, that a past or future being is you only if she is then psychologically continuous with you and no other being is. (There is no circularity in this. We need not know the answer to the persistence question in order to know how many people there are at any one time; that comes under the population question.) This means that neither Lefty nor Righty is you. They both come into existence when your cerebrum is divided. If both your cerebral hemispheres are transplanted, you cease to exist—though you would survive if only one were transplanted and the other destroyed. Fission is death. (Shoemaker 1984: 85, Parfit 1984: 207; 2012: 6f., Unger 1990: 265, Garrett 1998: ch. 4). 