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Eliezer Yudkowsky, “Harry Potter and the Methods of Rationality”
Recognition code 927, I am a potato

And another piece of paper popped into his hand. Harry took it out, staring at it. It too was in his own handwriting. The note said:

Dear Me,
Please play the game. You can only play the game once in a lifetime. This is an irreplaceable opportunity.
Recognition code 927, I am a potato.
Yours,
You.

Harry nodded slowly. «Recognition code 927, I am a potato» was indeed the message he had worked out in advance — some years earlier, while watching TV — that only he would know. If he had to identify a duplicate of himself as being really him, or something. Just in case. Be Prepared.
discourse, line, memory, mind