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arXiv · 2107.01299

Extending Properly n-REA Sets

Peter A. Cholak·Peter M. Gerdes
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Abstract

In [5] Soare and Stob prove that if $A$ is an r.e. set which isn't computable then there is a set of the form $A \oplus W^A_e$ which isn't of r.e. Turing degree. If we define a properly $n+1$-REA set to be an $n+1$-REA set which isn't Turing equivalent to any $n$-REA set this result shows that every properly 1-REA set can be extended to a properly 2-REA set. This result was extended in [1] by Cholak and Hinman who proved that every 2-REA set can be extended to a properly 3-REA set. This leads naturally to the hypothesis that every properly $n$-REA set can be extended to a properly $n+1$-REA set. In this paper, we show this hypothesis is false and that there is a properly $3$-REA set which can't be extended to a properly $4$-REA set.

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BibTeXRIS

Peter A. Cholak, Peter M. Gerdes. 2021-07-02. Extending Properly n-REA Sets. https://doi.org/10.3233/com-210362

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