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Annals of Pure and Applied Logic
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The minimal e-degree problem in fragments of Peano arithmetic

Authors: Arslanov, M.M.; Chong, C.T.; Cooper, S.B.; Yang, Y.;

The minimal e-degree problem in fragments of Peano arithmetic

Abstract

The paper presents several results concerning the e-degrees over models of fragments of Peano Arithmetic. By an unpublished result of \textit{L. Gutteridge} [Some results on enumeration reducibility. Ph.D. Thesis, Simon Fraser Univ. (1971)], there is no minimal e-degree for the standard model. The authors extend this to regular sets in models of \(B\Sigma_2\). A subset of a model \(M\) is called \textit{regular}, if its intersection with any interval \([0,a]\) in \(M\) is \(M\)-finite. An e-degree is regular, if it contains a regular set. It is shown that there are no \(\Delta_2\) minimal e-degrees in models of \(B\Sigma_2\), and that any regular minimal e-degree in a model of \(B\Sigma_2\) is \(\Delta_2\). Hence, if a model of \(B\Sigma_2\) has a minimal e-degree, it cannot be regular. If \(M\) is a model of \(I\Sigma_2\), then \(M\) has a minimal e-degree iff it is standard, and, if \(M\) is nonstandard, then every cut in \(M\) is of a minimal degree. The situation is different under \(B\Sigma_2\). A \(B\Sigma_2\) model is a model of \(B\Sigma_2+\lnot I\Sigma_2\). There is a \(B\Sigma_2\) model in which no \(\Sigma_2\) cut is of a minimal e-degree, and there is one whose all \(\Sigma_2\) cuts have a minimal e-degree. The paper concludes with a list of open problems and a conjecture that there is a minimal e-degree in every \(B\Sigma_2\) model.

Keywords

First-order arithmetic and fragments, Models of arithmetic and set theory, Nonstandard models of arithmetic, Logic, \(\Sigma_2\)-collection, e-degrees, Other degrees and reducibilities in computability and recursion theory, fragments of arithemtic, 510, 004

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selected citations
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This is an alternative to the "Influence" indicator, which also reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Citations provided by BIP!
popularity
This indicator reflects the "current" impact/attention (the "hype") of an article in the research community at large, based on the underlying citation network.
BIP!Popularity provided by BIP!
influence
This indicator reflects the overall/total impact of an article in the research community at large, based on the underlying citation network (diachronically).
BIP!Influence provided by BIP!
impulse
This indicator reflects the initial momentum of an article directly after its publication, based on the underlying citation network.
BIP!Impulse provided by BIP!
0
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