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Classes of Polish spaces under effective Borel isomorphism

About this Title

Vassilios Gregoriades, Technische Universität Darmstadt, Fachbereich Mathematik, Arbeitsgruppe Logik, Schloßgartenstraße 7, 64289 Darmstadt, Germany

Publication: Memoirs of the American Mathematical Society
Publication Year: 2016; Volume 240, Number 1135
ISBNs: 978-1-4704-1563-1 (print); 978-1-4704-2822-8 (online)
DOI: https://doi.org/10.1090/memo/1135
Published electronically: October 9, 2015
Keywords: Recursively presented metric space, effective Borel isomorphism, $\Delta ^1_1$ isomorphism, $\Delta ^1_1$ injection, Kleene space, Spector-Gandy space.
MSC: Primary 03E15, 03D30, 03D60

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Table of Contents

Chapters

  • Preface
  • 1. Introduction
  • 2. The spaces $\mathcal {N}^{T}$
  • 3. Kleene spaces
  • 4. Characterizations of $\mathcal {N}$ up to $\Delta ^1_1$ isomorphism
  • 5. Spector-Gandy spaces
  • 6. Questions and related results

Abstract

We study the equivalence classes under $\Delta ^1_1$ isomorphism, otherwise effective Borel isomorphism, between complete separable metric spaces which admit a recursive presentation and we show the existence of strictly increasing and strictly decreasing sequences as well as of infinite antichains under the natural notion of $\Delta ^1_1$-reduction, as opposed to the non-effective case, where only two such classes exist, the one of the Baire space and the one of the naturals. A key tool for our study is a mapping $T \mapsto \mathcal {N}^{T}$ from the space of all trees on the naturals to the class of Polish spaces, for which every recursively presented space is $\Delta ^1_1$-isomorphic to some $\mathcal {N}^{T}$ for a recursive $T$, so that the preceding spaces are representatives for the classes of $\Delta ^1_1$ isomorphism. We isolate two large categories of spaces of the type $\mathcal {N}^{T}$, the Kleene spaces and the Spector-Gandy spaces and we study them extensively. Moreover we give results about hyperdegrees in the latter spaces and characterizations of the Baire space up to $\Delta ^1_1$ isomorphism.

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