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Transactions of the American Mathematical Society

Published by the American Mathematical Society since 1900, Transactions of the American Mathematical Society is devoted to longer research articles in all areas of pure and applied mathematics.

ISSN 1088-6850 (online) ISSN 0002-9947 (print)

The 2020 MCQ for Transactions of the American Mathematical Society is 1.48.

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Borel classes and closed games: Wadge-type and Hurewicz-type results
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by A. Louveau and J. Saint-Raymond PDF
Trans. Amer. Math. Soc. 304 (1987), 431-467 Request permission

Abstract:

For each countable ordinal $\xi$ and pair $({A_0}, {A_1})$ of disjoint analytic subsets of ${2^\omega }$, we define a closed game ${J_\xi }({A_0}, {A_1})$ and a complete $\Pi _\xi ^0$ subset ${H_\xi }$ of ${2^\omega }$ such that (i) a winning strategy for player I constructs a $\sum _\xi ^0$ set separating ${A_0}$ from ${A_1}$; and (ii) a winning strategy for player II constructs a continuous map $\varphi :{2^\omega } \to {A_0} \cup {A_1}$ with ${\varphi ^{ - 1}}({A_0}) = {H_\xi }$. Applications of this construction include: A proof in second order arithmetics of the statement "every $\Pi _\xi ^0$ non $\sum _\xi ^0$ set is $\Pi _\xi ^0$-complete"; an extension to all levels of a theorem of Hurewicz about $\sum _2^0$ sets; a new proof of results of Kunugui, Novikov, Bourgain and the authors on Borel sets with sections of given class; extensions of results of Stern and Kechris. Our results are valid in arbitrary Polish spaces, and for the classes in Lavrentieff’s and Wadge’s hierarchies.
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Additional Information
  • © Copyright 1987 American Mathematical Society
  • Journal: Trans. Amer. Math. Soc. 304 (1987), 431-467
  • MSC: Primary 03E15; Secondary 04A15, 28A05, 54H05
  • DOI: https://doi.org/10.1090/S0002-9947-1987-0911079-0
  • MathSciNet review: 911079