Journal of Symbolic Logic

Located Sets and Reverse Mathematics

Mariagnese Giusto and Stephen G. Simpson

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Let X be a compact metric space. A closed set K $\subseteq$ X is located if the distance function d(x, K) exists as a continuous real-valued function on X; weakly located if the predicate d(x, K) $>$ r is $\Sigma^0_1$ allowing parameters. The purpose of this paper is to explore the concepts of located and weakly located subsets of a compact separable metric space in the context of subsystems of second order arithmetic such as RCA$_0$, WKL$_0$ and ACA$_0$. We also give some applications of these concepts by discussing some versions of the Tietze extension theorem. In particular we prove an RCA$_0$ version of this result for weakly located closed sets.

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J. Symbolic Logic, Volume 65, Issue 3 (2000), 1451-1480.

First available in Project Euclid: 6 July 2007

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Giusto, Mariagnese; Simpson, Stephen G. Located Sets and Reverse Mathematics. J. Symbolic Logic 65 (2000), no. 3, 1451--1480.

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