Joanna Jureczko: Some remarks on Kuratowski partitions, new results

Tuesday, May 9, 2017, 17:15
Wrocław University of Technology, 215 D-1

Speaker: Joanna Jureczko (Cardinal Stefan Wyszynski University in Warsaw)

Title: Some remarks on Kuratowski partitions, new results


K. Kuratowski in 1935 posed the problem whether a function $f \colon X \to Y$ from a completely metrizable space $X$ to a metrizable space $Y$ is continuous apart from a meager set.
This question is equivalent to the question about the existence of so called a Kuratowski partition, i. e. a partition $\mathcal{F}$ of a space $X$ into meager sets such that $\bigcup \mathcal{F}’$ for any $\mathcal{F}’ \subset \mathcal{F}$.
With any Kuratowski partition we may associate a $K$-ideal, i.e. an ideal of the form
$$I_{\mathcal{F}} = \{A \subset \kappa \colon \bigcup_{\alpha \in A}F_\alpha \textrm{ is meager }, F_\alpha \in \mathcal{F}\}.$$
It would seem that the information about $I_{\mathcal{F}}$ would give us full information about the ideal and the world in which it lives.
My talk is going to show that it is big simplification and localization technique from a Kuratowski partition cannot be omitted but the proof can be much simplier.
During the talk I will show among others a new proof of non-existence of a Kuratowski partition in Ellentuck topology and a new combinatorial proof of Frankiewicz – Kunen Theorem (1987) on the existence of measurable cardinals.

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