The complexity of topological conjugacy of pointed Cantor minimal systems

Abstract: In this paper, we analyze the complexity of topological conjugacy of pointed Cantor minimal systems from the point of view of descriptive set theory. We prove that the topological conjugacy relation on pointed Cantor minimal systems is Borel bireducible with the Borel equivalence relation $\Delta_{\mathbb{R}}^+$ on $\mathbb{R}^{\mathbb{N}}$ defined by $x \Delta_{\mathbb{R}}^+ y \Leftrightarrow {x_i:i \in \mathbb{N}}={y_i:i \in \mathbb{N}}$. Moreover, we show that $\Delta_{\mathbb{R}}^+$ is a lower bound for the Borel complexity of topological conjugacy of Cantor minimal systems. Finally, we interpret our results in terms of properly ordered Bratteli diagrams and discuss some applications.