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Semialgebraic universal covers of normal projective varieties

OpenAI · September 24, 2026

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Abstract

We prove the Kollár–Pardon conjecture: the universal cover of a connected normal projective complex variety is biholomorphic to a semialgebraic open subset of a projective variety if and only if it is a product of a bounded symmetric domain, a complex affine space, and a simply connected normal projective variety.

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Cite

@misc{OAI:Semialgebraic-universal-covers-of-normal-projective-varieties-September-24-2026,
  author = {{OpenAI}},
  title = {{Semialgebraic universal covers of normal projective varieties}},
  howpublished = {OpenAI Math Release preprint
                  \href{https://github.com/openai/math/blob/main/preprints/Semialgebraic-universal-covers-of-normal-projective-varieties-September-24-2026/paper.pdf}{OAI:Semialgebraic-universal-covers-of-normal-projective-varieties-September-24-2026}},
  year = {2026}
}

Lean formalization

OpenAI provides Lean files for this family: lean/docs/058.md. The Lean statements have not been checked by people against the paper's claims.

Family 058: Semialgebraic universal covers and bounded domains

Proves the Kollár–Pardon conjecture: the semialgebraic universal covers of connected normal projective complex varieties are exactly products $D\times\mathbb C^m\times F$, with D bounded symmetric and F simply connected, normal, and projective. A universal cover is quasi-projective exactly when the bounded symmetric factor is absent. In particular, a smooth projective variety covered by ℂn has a finite étale cover by an abelian variety.

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