Infinite games and cardinal properties of topological spaces

TL;DR

This paper explores how topological games can be used to establish bounds on the cardinality of various classes of topological spaces, providing new insights and partial answers to longstanding questions.

Contribution

It introduces game-theoretic methods to derive bounds on space cardinalities and addresses open questions in topology using these techniques.

Findings

Bound the cardinality of weakly Lindelöf first-countable regular spaces.

Prove a game-theoretic version of cellularity and derive bounds.

Show Hajnal-Juhász bound applies to almost regular non-Hausdorff spaces.

Abstract

Inspired by work of Scheepers and Tall, we use properties defined by topological games to provide bounds for the cardinality of topological spaces. We obtain a partial answer to an old question of Bell, Ginsburg and Woods regarding the cardinality of weakly Lindel\"of first-countable regular spaces and answer a question recently asked by Babinkostova, Pansera and Scheepers. In the second part of the paper we study a game-theoretic version of cellularity, a special case of which has been introduced by Aurichi. We obtain a game-theoretic proof of Shapirovskii's bound for the number of regular open sets in an (almost) regular space and give a partial answer to a natural question about the productivity of a game strengthening of the countable chain condition that was introduced by Aurichi. As a final application of our results we prove that the Hajnal-Juh\'asz bound for the cardinality of a first-countable ccc Hausdorff space is true for almost regular (non-Hausdorff) spaces.