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Difference between revisions of "Turing reducibility"

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A relation between sets of natural numbers.  We say that $A$ is Turing reducible to $B$, $A \le_{\mathrm{T}} B$, if there is a [[Turing machine]] for the decision problem $x \in A$ given an auxiliary tape which encodes the answers to all questions $y \in B$.  Such a tape is often described as an "oracle" or "black box" for the problem of membership of $B$.  This defines a [[pre-order]] on sets of natural numbers:Turing reduction may also be regarded as a relation between functions on natural numbers: in this case, the [[characteristic function]]s of sets of natural numbers.
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A relation between sets of natural numbers.  We say that $A$ is Turing reducible to $B$, $A \le_{\mathrm{T}} B$, if there is a [[Turing machine]] for the decision problem $x \in A$ given an auxiliary tape which encodes the answers to all questions $y \in B$.  Such a tape is often described as an "oracle" or "black box" for the problem of membership of $B$.  This defines a [[pre-order]] on sets of natural numbers:Turing reduction may also be regarded as a relation between functions on natural numbers: in this case, the [[characteristic function]]s of sets of natural numbers.  The equivalence relation $A \equiv_{\mathrm{T}} B$ if $A \le_{\mathrm{T}} B$ and $B \le_{\mathrm{T}} A$ is ''Turing equivalence'' and the equivalence classes are the ''[[Turing degree]]s''.  Turing reducibility defines an partial order on the Turing degrees.
  
 
====References====
 
====References====
* Nies, André ''Computability and randomness'' Oxford Logic Guides '''51''' Oxford University Press (2009)  ISBN 0-19-923076-1 {{ZBL|1169.03034}}
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* Nies, André ''Computability and randomness'' Oxford Logic Guides '''51''' Oxford University Press (2009)  {{ISBN|0-19-923076-1}} {{ZBL|1169.03034}}
* Pippenger, Nicholas ''Theories of Computability'' Cambridge University Press (1997) ISBN 0-521-55380-6 {{ZBL|1200.03025}}
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* Pippenger, Nicholas ''Theories of Computability'' Cambridge University Press (1997) {{ISBN|0-521-55380-6}} {{ZBL|1200.03025}}

Latest revision as of 19:32, 17 November 2023

A relation between sets of natural numbers. We say that $A$ is Turing reducible to $B$, $A \le_{\mathrm{T}} B$, if there is a Turing machine for the decision problem $x \in A$ given an auxiliary tape which encodes the answers to all questions $y \in B$. Such a tape is often described as an "oracle" or "black box" for the problem of membership of $B$. This defines a pre-order on sets of natural numbers:Turing reduction may also be regarded as a relation between functions on natural numbers: in this case, the characteristic functions of sets of natural numbers. The equivalence relation $A \equiv_{\mathrm{T}} B$ if $A \le_{\mathrm{T}} B$ and $B \le_{\mathrm{T}} A$ is Turing equivalence and the equivalence classes are the Turing degrees. Turing reducibility defines an partial order on the Turing degrees.

References

  • Nies, André Computability and randomness Oxford Logic Guides 51 Oxford University Press (2009) ISBN 0-19-923076-1 Zbl 1169.03034
  • Pippenger, Nicholas Theories of Computability Cambridge University Press (1997) ISBN 0-521-55380-6 Zbl 1200.03025
How to Cite This Entry:
Turing reducibility. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Turing_reducibility&oldid=37578