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U(n,x) is Gödel universal function, and we need to show {n:U(n,x) is defined for all x} is not enumerable. I do not have any clue right now. Anyone can give me some hint about this question.

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marked as duplicate by Ran G., Luke Mathieson, Kaveh, Juho, Gilles Jun 7 '15 at 16:50

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