The descriptive complexity of the set of all closed zero-dimensional subsets of a Polish space

Abstract

Given a space $X$ we investigate the descriptive complexity class $\G_X$ of the set $\FF_0(X)$ of all its closed zero-dimensional subsets, viewed as a subset of the hyperspace $\FF(X)$ of all closed subsets of $X$. We prove that $\max \{ \G_X; \ X \text{ analytic } \}=\pca $ and $\sup \{ \G_X; \ X \text{ Borel } \borm ξ\} \supseteq \Game \bora ξ$ for any countable ordinal $\xi \ge 1$. In particular we prove that there exists a one-dimensional Polish subpace of $2^\wo\times \R^2$ for which $\FF_0(X)$ is not in the smallest non trivial pointclass closed under complementation and the Souslin operation $\mathcal{A}$.