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COUNTABLY PERFECTLY MEAGER SETS

Published online by Cambridge University Press:  07 June 2021

ROMAN POL
Affiliation:
INSTITUTE OF MATHEMATICS UNIVERSITY OF WARSAW, UL. BANACHA 2 02-097 WARSAW, POLAND E-mail: pol@mimuw.edu.pl E-mail: piotrzak@mimuw.edu.pl
PIOTR ZAKRZEWSKI
Affiliation:
INSTITUTE OF MATHEMATICS UNIVERSITY OF WARSAW, UL. BANACHA 2 02-097 WARSAW, POLAND E-mail: pol@mimuw.edu.pl E-mail: piotrzak@mimuw.edu.pl

Abstract

We study a strengthening of the notion of a perfectly meager set. We say that a subset A of a perfect Polish space X is countably perfectly meager in X, if for every sequence of perfect subsets $\{P_n: n \in \mathbb N\}$ of X, there exists an $F_\sigma $-set F in X such that $A \subseteq F$ and $F\cap P_n$ is meager in $P_n$ for each n. We give various characterizations and examples of countably perfectly meager sets. We prove that not every universally meager set is countably perfectly meager correcting an earlier result of Bartoszyński.

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Type
Article
Copyright
© Association for Symbolic Logic 2021

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