Dorias, FG, Dzhafarov, DD, Hirst, JL et al. (2 more authors) (2016) On uniform relationships between combinatorial problems. Transactions of the American Mathematical Society, 368 (2). pp. 13211359. ISSN 00029947
Abstract
The enterprise of comparing mathematical theorems according to their logical strength is an active area in mathematical logic, with one of the most common frameworks for doing so being reverse mathematics. In this setting, one investigates which theorems provably imply which others in a weak formal theory roughly corresponding to computable mathematics. Since the proofs of such implications take place in classical logic, they may in principle involve appeals to multiple applications of a particular theorem, or to nonuniform decisions about how to proceed in a given construction. In practice, however, if a theorem Q implies a theorem P, it is usually because there is a direct uniform translation of the problems represented by P into the problems represented by Q, in a precise sense formalized by Weihrauch reducibility. We study this notion of uniform reducibility in the context of several natural combinatorial problems, and compare and contrast it with the traditional notion of implication in reverse mathematics. We show, for instance, that for all n; j; k 1, if j < k then Ramsey's theorem for ntuples and k many colors is not uniformly, or Weihrauch, reducible to Ramsey's theorem for ntuples and j many colors. The two theorems are classically equivalent, so our analysis gives a genuinely ner metric by which to gauge the relative strength of mathematical propositions. We also study Weak K�onig's Lemma, the Thin Set Theorem, and the Rainbow Ramsey's Theorem, along with a number of their variants investigated in the literature. Weihrauch reducibility turns out to be connected with sequential forms of mathematical principles, where one wishes to solve in nitely many instances of a particular problem simultaneously. We exploit this connection to uncover new points of di erence between combinatorial problems previously thought to be more closely related.
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Copyright, Publisher and Additional Information:  © 2015 American Mathematical Society. First published in Transactions of the American Mathematical Society in 368 (2), 2015, published by the American Mathematical Society. This is an author produced version of a paper , uploaded in accordance with the publisher's selfarchiving policy. 
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Institution:  The University of Leeds 
Academic Units:  The University of Leeds > Faculty of Maths and Physical Sciences (Leeds) > School of Mathematics (Leeds) > Pure Mathematics (Leeds) 
Depositing User:  Symplectic Publications 
Date Deposited:  24 Feb 2017 12:47 
Last Modified:  28 Jan 2018 18:42 
Published Version:  https://doi.org/10.1090/tran/6465 
Status:  Published 
Publisher:  American Mathematical Society 
Identification Number:  https://doi.org/10.1090/tran/6465 