Draft:Relativization (Complexity Theory)

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Relativization is a fundamental technique in the study of complexity theory and cryptography. It refers to the process of modifying complexity classes by incorporating an "oracle", either as the input or part of the definition of language. We call a result about complexity classes "relativize" if the result mains true even if the complexity class involved in the result is replaced with the respective classes relative to any oracle. All known complexity results made by standard "black box" reduction relativize. On the contrary, there is a few complexity theoretic statements cannot relativize, which means they are true relative to certain oracles and false relative to certain others. The proof on the non-relativization of a statement can be used as an evidence for the difficulty of redolving questions in complexity theory [BGS75][BG81], because it indicates that no techniques which relativizes can prove the statement.


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