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Finite Monoid Computations and a Uniform Generalized Star-Height Bound

OpenAI · September 25, 2026

Lean

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Abstract

Every regular language over a finite alphabet has a generalized regular expression of star height at most thirteen over that same alphabet. We prove this uniform bound by representing finite monoid computations as affine updates and recovering them through twelve successive split constructions.

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Notes

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Formalization

Possibly relevant literature (found by the agent, not checked)

  • Jean-Éric Pin, Open problems about regular languages, 35 years later (talk slides, Brzozowski 80, 2015-06-24). Slides 9–10 note that no language of generalized star height greater than one was known and recall that if the height-at-most-one languages form a variety then all regular languages have height at most one; this bears on the paper's distinction between uniform boundedness and the height-one question.

Digests and expositions

Elsewhere

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Cite

@misc{OAI:Finite-Monoid-Computations-and-a-Uniform-Generalized-Star-Height-Bound-September-25-2026,
  author = {{OpenAI}},
  title = {{Finite Monoid Computations and a Uniform Generalized Star-Height Bound}},
  howpublished = {OpenAI Math Release preprint
                  \href{https://github.com/openai/math/blob/main/preprints/Finite-Monoid-Computations-and-a-Uniform-Generalized-Star-Height-Bound-September-25-2026/Finite-Monoid-Computations-and-a-Uniform-Generalized-Star-Height-Bound-September-25-2026.pdf}{OAI:Finite-Monoid-Computations-and-a-Uniform-Generalized-Star-Height-Bound-September-25-2026}},
  year = {2026}
}

Lean formalization

OpenAI provides Lean files for this family: lean/docs/134.md. The Lean statements have not been checked by people against the paper's claims.

Family 134: Generalized star height at most three

Every regular language over a finite alphabet has a generalized regular expression with at most three nested Kleene stars, allowing union, concatenation and complement over the same alphabet. This establishes an absolute bound independent of automaton size, resolving the uniform-boundedness version of the generalized star-height problem.

Other papers in this family: