The descriptive complexity of the set of all closed zero-dimensional subsets of a Polish space (1805.06732v1)

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 $\sup { \G_X; \ X \text{ Borel } \borm \xi} \supseteq \Game \bora \xi$ for any countable ordinal $\xi\geq1$. 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 $\mathcal A\,$.