### On the Computability of the Topological Entropy of Subshifts

*Jakob Grue Simonsen*

#### Abstract

We prove that the topological entropy of subshifts having decidable language is uncomputable in the following sense:
For no error bound less than 1/4 does there exists a program that, given a decision procedure for the language of a
subshift as input, will approximate the entropy of the subshift within the error bound. In addition, we prove that not
only is the topological entropy of sofic shifts computable to arbitary precision (a well-known fact), but all standard
comparisons of the topological entropy with rational numbers are decidable.

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