Generalized Choquet spaces

Samuel Coskey, Philipp Schlicht
2015 Fundamenta Mathematicae  
We introduce an analog to the notion of Polish space for spaces of weight ≤κ, where κ is an uncountable regular cardinal such that κ^<κ=κ. Specifically, we consider spaces in which player II has a winning strategy in a variant of the strong Choquet game which runs for κ many rounds. After discussing the basic theory of these games and spaces, we prove that there is a surjectively universal such space and that there are exactly 2^κ many such spaces up to homeomorphism. We also establish a
more » ... ski-like theorem that under mild hypotheses, any two such spaces of size >κ are isomorphic by a κ-Borel function. We then consider a dynamic version of the Choquet game and show that in this case the existence of a winning strategy for player II implies the existence of a winning tactic, that is, a strategy that depends only on the most recent move. We also study a generalization of Polish ultrametric spaces where the ultrametric is allowed to take values in a set of size κ. We show that in this context, there is a family of universal Urysohn-type spaces, and we give a characterization of such spaces which are hereditarily κ-Baire.
doi:10.4064/fm924-12-2015 fatcat:5n3zbc7vafcbdaqt265jetspbq