How do we find out who is who?
What evidence bears on the question of whether the person here now is the one who was here yesterday?
What ought we to do when different kinds of evidence support opposing verdicts?
One source of evidence is first-person memory: if you remember doing something, or at least seem to remember, it was probably you who did it. Another source is physical continuity: if the person who did it looks just like you, or even better if she is in some sense physically or spatio-temporally continuous with you, that is reason to think she is you. Which of these sources is more fundamental?
Does first-person memory count as evidence all by itself, for instance, or only insofar as we can check it against publicly available physical evidence?