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arXiv · 2409.12068

The repetition threshold for ternary rich words

James D. Currie·Lucas Mol·Jarkko Peltomäki
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Abstract

In 2017, Vesti proposed the problem of determining the repetition threshold for infinite rich words, i.e., for infinite words in which all factors of length $n$ contain $n$ distinct nonempty palindromic factors. In 2020, Currie, Mol, and Rampersad proved a conjecture of Baranwal and Shallit that the repetition threshold for binary rich words is $2 + \sqrt{2}/2$. In this paper, we prove a structure theorem for $16/7$-power-free ternary rich words. Using the structure theorem, we deduce that the repetition threshold for ternary rich words is $1 + 1/(3 - μ) \approx 2.25876324$, where $μ$ is the unique real root of the polynomial $x^3 - 2x^2 - 1$.

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James D. Currie, Lucas Mol, Jarkko Peltomäki. 2025-05-30. The repetition threshold for ternary rich words. https://arxiv.org/abs/2409.12068

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