Suffix conjugates for a class of morphic subshifts

TL;DR

This paper introduces suffix conjugates for a class of morphic subshifts, establishing a conjugacy with a topological dynamical system and demonstrating the sofic nature for Fibonacci and Thue-Morse morphisms.

Contribution

It constructs suffix conjugates for morphic subshifts under certain conditions and proves they are sofic for specific well-known morphisms.

Findings

Suffix conjugates form a topological dynamical system.

Conjugacy between the subshift and the suffix conjugate is established.

Fibonacci and Thue-Morse cases are shown to be sofic.

Abstract

Let A be a finite alphabet and f: A^* --> A^* be a morphism with an iterative fixed point f^\omega(\alpha), where \alpha{} is in A. Consider the subshift (X, T), where X is the shift orbit closure of f^\omega(\alpha) and T: X --> X is the shift map. Let S be a finite alphabet that is in bijective correspondence via a mapping c with the set of nonempty suffixes of the images f(a) for a in A. Let calS be a subset S^N be the set of infinite words s = (s_n)_{n\geq 0} such that \pi(s):= c(s_0)f(c(s_1)) f^2(c(s_2))... is in X. We show that if f is primitive and f(A) is a suffix code, then there exists a mapping H: calS --> calS such that (calS, H) is a topological dynamical system and \pi: (calS, H) --> (X, T) is a conjugacy; we call (calS, H) the suffix conjugate of (X, T). In the special case when f is the Fibonacci or the Thue-Morse morphism, we show that the subshift (calS, T) is sofic, that is, the language of calS is regular.