Simple strategies for Banach–Mazur games and sets of probability 1

Abstract

In 2006, Varacca and Völzer proved that on finite graphs, ω-regular large sets coincide with ω-regular sets of probability 1, by using the existence of positional strategies in the related Banach–Mazur games. Motivated by this result, we try to understand relations between sets of probability 1 and various notions of simple strategies (including those introduced in a recent paper of Grädel and Leßenich). Then, we introduce a generalisation of the classical Banach–Mazur game and in particular, a probabilistic version whose goal is to characterise sets of probability 1 (as classical Banach–Mazur games characterise large sets). We obtain a determinacy result for these games, when the winning set is a countable intersection of open sets.