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RAMSEY-LIKE THEOREMS AND MODULI OF COMPUTATION

Part of: Computability and recursion theory General logic

Published online by Cambridge University Press:  27 October 2020

LUDOVIC PATEY
LUDOVIC PATEY*
Affiliation:
CN RS, INSTITUT CAMILLE JORDAN UNIVERSITÉ CLAUDE BERNARD LYON 1 43 BOULEVARD DU 11 NOVEMBRE 1918 F-69622 VILLEURBANNE CEDEX, FRANCEE-mail: ludovic.patey@computability.frURL: http://ludovicpatey.com
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Abstract

Ramsey’s theorem asserts that every k-coloring of $[\omega ]^n$ admits an infinite monochromatic set. Whenever $n \geq 3$ , there exists a computable k-coloring of $[\omega ]^n$ whose solutions compute the halting set. On the other hand, for every computable k-coloring of $[\omega ]^2$ and every noncomputable set C, there is an infinite monochromatic set H such that $C \not \leq _T H$ . The latter property is known as cone avoidance.

In this article, we design a natural class of Ramsey-like theorems encompassing many statements studied in reverse mathematics. We prove that this class admits a maximal statement satisfying cone avoidance and use it as a criterion to re-obtain many existing proofs of cone avoidance. This maximal statement asserts the existence, for every k-coloring of $[\omega ]^n$ , of an infinite subdomain $H \subseteq \omega $ over which the coloring depends only on the sparsity of its elements. This confirms the intuition that Ramsey-like theorems compute Turing degrees only through the sparsity of its solutions.

Keywords

Ramsey’s theoryreverse mathematicscomputability theorymodulus

MSC classification

Primary: 03B30: Foundations of classical theories (including reverse mathematics)
Secondary: 03D80: Applications of computability and recursion theory
Type
Article
Information
The Journal of Symbolic Logic , Volume 87 , Issue 1 , March 2022 , pp. 72 - 108
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Copyright
© The Author(s), 2020. Published by Cambridge University Press on behalf of The Association for Symbolic Logic

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