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Taming implies compatibility on four-manifolds

OpenAI · October 6, 2026

Lean

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Abstract

We prove that every smooth almost complex structure on a closed four-manifold which is tamed by a symplectic form is compatible with a symplectic form. This gives a positive solution to Donaldson's tamed-to-compatible conjecture. We also characterize the compatible cone by strict intersection positivity on the closure of the invariant part of the taming cone.

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Notes

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work in progress

Collected automatically by AI tools (Claude Opus 5.5 and GPT-6 Astra, 2026-10-21) and not checked by a person. May be wrong or incomplete. Report an error.

Follow-up works

  • OpenAI, Deforming hypersymplectic four-manifolds to hyperkähler triples (OpenAI Math Release preprint, 2026-10-07). This companion manuscript explicitly reuses the taming paper’s current estimates and density-splitting argument, adding prescribed-class arguments under closed definite-pair and $b^+=3$ hypotheses for its claimed hypersymplectic deformation theorem. [AI-generated per source]

Formalization

  • OpenAI math release, Lean scope note for family 342 (Donaldson's tamed-to-compatible conjecture) (lean/docs/342.md, 2026). The release's scope note says the formalized result covers every closed connected smooth four-manifold with $J$ fixed, with no integrability assumption and no prescribed cohomology class; it links the September 23 edition of the paper and its comparator statement. [cites earlier version]
  • OpenAI, TamingCompatibility.lean (openai/math, lean/ComparatorChallenges, 2026). A 68-line Lean 4/Mathlib Comparator statement of Theorem 1.1 (taming_implies_compatibility) for compact connected manifolds modelled on $\mathbb R^4$, with its own definitions of two-forms, closedness via pullbacks to charts, taming and compatibility; the proof in this statement file is sorry.

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Cite

@misc{OAI:Taming-implies-compatibility-on-four-manifolds-October-6-2026,
  author = {{OpenAI}},
  title = {{Taming implies compatibility on four-manifolds}},
  howpublished = {OpenAI Math Release preprint
                  \href{https://github.com/openai/math/blob/main/preprints/Taming-implies-compatibility-on-four-manifolds-October-6-2026/paper.pdf}{OAI:Taming-implies-compatibility-on-four-manifolds-October-6-2026}},
  year = {2026}
}

Versions

This version characterizes the compatible cone by intersection positivity, restricts the cone-sum equality to $h_J^-=b_2^+-1$, and adds a four-torus example of strict inclusion; see the previous version.

Lean formalization

OpenAI provides Lean files for this family: lean/docs/342.md. The Lean statements have not been checked by people against the paper's claims.

Family 342: Donaldson's tamed-to-compatible conjecture

Proves Donaldson's tamed-to-compatible conjecture: every smooth almost complex structure on a closed four-manifold that is tamed by a symplectic form admits a compatible symplectic form. The almost complex structure stays fixed; the form's cohomology class may change.

This is the only paper in this family.