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The entropy-rate dimension formula for self-similar measures on the line

OpenAI · September 24, 2026

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Abstract

We prove that the Hausdorff dimension of every finite real self-similar measure equals the minimum of one and its random-walk entropy rate divided by its Lyapunov exponent. Exact overlaps are allowed, and the contraction ratios may be unequal and negative. This resolves the entropy-rate dimension conjecture.

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News and blogs

  • MINT Lab, Yesterday in AI · 6 October 2026 (newsletter, Oct 2026). Covers the Kittle–Kogler preprint as "a concrete case of parallel discovery", citing OpenAI's proof claimed on 24 September and public on 6 October, and Kittle–Kogler's found on 27 September and posted on 7 October. [AI-generated per source]

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Cite

@misc{OAI:The-entropy-rate-dimension-formula-for-self-similar-measures-on-the-line-September-24-2026,
  author = {{OpenAI}},
  title = {{The entropy-rate dimension formula for self-similar measures on the line}},
  howpublished = {OpenAI Math Release preprint
                  \href{https://github.com/openai/math/blob/main/preprints/The-entropy-rate-dimension-formula-for-self-similar-measures-on-the-line-September-24-2026/main.pdf}{OAI:The-entropy-rate-dimension-formula-for-self-similar-measures-on-the-line-September-24-2026}},
  year = {2026}
}

Lean formalization

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Family 148: The entropy-rate dimension formula for self-similar measures

For every self-similar measure on the line generated by finitely many contracting similarities, proves $\dim_{\mathrm H}\mu=\min\{1,h_{\mathrm{RW}}/\chi\}$, where $h_{\mathrm{RW}}$ is the entropy rate of random composed maps and χ the average logarithmic contraction. This resolves the entropy-rate dimension conjecture without a separation assumption, allowing exact overlaps and unequal contraction ratios.

This is the only paper in this family.