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  "body": "\n## Summary\n\nAn oracle machine is a [[Turing machine|758EYCN27B]] with an extra device, the oracle, that answers questions of the form \"is $n$ in the set $O$?\" in a single step.\nThe set $O$ can be any set of natural numbers, even an uncomputable one.\nOracle machines define relative computability: what can be computed if some set is given for free.\nThey are used to define Turing reduction, Turing degrees and the Turing jump.\n\n## Explanations\n\n### L1 human\n\nAn oracle machine is an ordinary computer program with a phone line to an all-knowing helper.\nThe helper knows one fixed set $O$ and answers only yes-or-no questions about it.\nThe program writes a number, calls the helper, and gets the answer immediately.\nFor example, with the set of halting programs as oracle, a program can decide whether any given program halts, which no ordinary program can do.\n",
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