Examples and Nonexamples of Distal Metric Structures

Abstract

This article provides examples of distal metric structures. One source of examples are metric valued fields. By analyzing indiscernible sequences, we show that real closed metric valued fields are distal, and conclude that algebraically closed metric valued fields, while stable, have the strong Erd\H{o}s-Hajnal property, which we define appropriately for metric structures. We find another example in topological dynamics: we study a metric structure whose automorphism group is the well-understood Polish group $\mathrm{Hom}^+([0,1])$ of increasing homeomorphisms of $[0,1]$. This was known to be NIP and highly unstable, and further properties were established in arXiv:1510.00238. We characterize models of its theory of this structure, which we call Dual Linear Continua, up to isomorphism. We analyze their indiscernible sequences and prove that they are distal, as well as constructing explicit distal cell decompositions.