Complexity Theory 6 . The Polynomial Hierarchy
نویسنده
چکیده
An oracle Turing machine M has the following additional features: – an additional tape (= query tape) – three additional states: query state q?, answer states qYES, qNO Suppose that M has an oracle for the problem A. Then the call of the oracle works as follows: If M is in state q?, then M decides if the string z on the query tape is a positive instance of A or not. ⇒ M either enters state qYES or qNO in one step. Notation. For any time complexity class C and oracle A (where A is either a problem or a class of problems) we write CA for the problems which can be decided by a TM within the time bound of C, where the TM is allowed to use an oracle for (any problem in the class) A. Examples. P, NP, P, NP, . . . ,
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