@misc{NB,
  author       = {{OpenAI}},
  title        = {{Rigidity of Smooth Billiards with a Continuous Caustic Collar}},
  howpublished = {OpenAI Math Release preprint
                  \href{https://github.com/openai/math/blob/main/preprints/Rigidity-of-Smooth-Billiards-with-a-Continuous-Caustic-Collar-September-24-2026/paper.pdf}{OAI:Rigidity-of-Smooth-Billiards-with-a-Continuous-Caustic-Collar-September-24-2026}},
  year         = {2026}
}

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