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Edit: "Whoever did the duplication" would be a better answer than "The guy who came first", admittedly. The duplicate and original would both believe themselves to be the original, or, if they are a rationalist, would probably withhold judgment.
More importantly, the question is terribly phrased - or just terrible. The philosopher could have started with "If you met the 'twins' afterwards, could someone tell them apart without asking anyone?", which has an obvious response of "no", and then gets followed by a actually interesting questions about, for example, what "memory" exactly is.
That version is a lot funnier, though!
You know what to do.
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