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DNR AND INCOMPARABLE TURING DEGREES

Part of: General logic Computability and recursion theory

Published online by Cambridge University Press:  06 April 2016

MINZHONG CAI ,
NOAM GREENBERG  and
MICHAEL MCINERNEY
MINZHONG CAI
Affiliation:
Department of Mathematics, Dartmouth College, Hanover, NH 03755, USA
NOAM GREENBERG
Affiliation:
School of Mathematics Statistics and Operations Research, Victoria University of Wellington, P.O. Box 600, Wellington, New Zealand
MICHAEL MCINERNEY
Affiliation:
School of Mathematics Statistics and Operations Research, Victoria University of Wellington, P.O. Box 600, Wellington, New Zealand

Abstract

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We construct an increasing ${\it\omega}$ -sequence $\langle \boldsymbol{a}_{n}\rangle$ of Turing degrees which forms an initial segment of the Turing degrees, and such that each $\boldsymbol{a}_{n+1}$ is diagonally nonrecursive relative to $\boldsymbol{a}_{n}$ . It follows that the DNR principle of reverse mathematics does not imply the existence of Turing incomparable degrees.

MSC classification

Primary: 03B30: Foundations of classical theories (including reverse mathematics)
Secondary: 03D28: Other Turing degree structures
Type
Research Article
Information
Forum of Mathematics, Sigma , Volume 4 , 2016 , e7
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Creative Commons
Creative Common License - CCCreative Common License - BY
This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.
Copyright
© The Author(s) 2016

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