Nilsequences and a structure theorem for topological dynamical systems

TL;DR

This paper characterizes inverse limits of nilsystems in topological dynamics, introduces a structure theorem analogous to measure-preserving systems, and applies it to identify nilsequences and construct maximal nilfactors.

Contribution

It provides a new structure theorem for topological dynamical systems and characterizes nilsequences through local properties, advancing understanding in ergodic theory and additive combinatorics.

Findings

Characterization of nilsequences via local properties

Construction of maximal nilfactors in distal minimal systems

Analog of the structure theorem for measure-preserving systems

Abstract

We characterize inverse limits of nilsystems in topological dynamics, via a structure theorem for topological dynamical systems that is an analog of the structure theorem for measure preserving systems. We provide two applications of the structure. The first is to nilsequences, which have played an important role in recent developments in ergodic theory and additive combinatorics; we give a characterization that detects if a given sequence is a nilsequence by only testing properties locally, meaning on finite intervals. The second application is the construction of the maximal nilfactor of any order in a distal minimal topological dynamical system. We show that this factor can be defined via a certain generalization of the regionally proximal relation that is used to produce the maximal equicontin uous factor and corresponds to the case of order 1.