Properties of Moebius number systems

TL;DR

This paper investigates Moebius number systems, focusing on tools for verifying their structure, exploring existence conditions, and examining when such systems are sofic, with partial results provided.

Contribution

It advances methods for proving subshift–iterative system pairs form Moebius number systems and explores existence and soficity conditions.

Findings

Improved tools for verifying Moebius number systems.

Partial results on existence conditions.

Brief discussion on soficity of Moebius number systems.

Abstract

Moebius number systems represent points using sequences of Moebius transformations. Thorough the paper, we are mainly interested in representing the unit circle (which is equivalent to representing R\cup\{\infty\}). The main aim of the paper is to improve already known tools for proving that a given subshift--iterative system pair is in fact a Moebius number system. We also study the existence problem: How to describe iterative systems resp. subshifts for which there exists a subshift resp. iterative system such that the resulting pair forms a Moebius number system. While we were unable to provide a complete answer to this question, we present both positive and negative partial results. As Moebius number systems are also subshifts, we can ask when a given Moebius number system is sofic. We give this problem a short treatment at the end of our paper.