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Lech's multiplicity conjecture

OpenAI · September 23, 2026

Lean

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Abstract

We prove Lech's multiplicity conjecture: Hilbert–Samuel multiplicity cannot decrease under a flat local homomorphism of nonzero Noetherian local rings. The result holds in arbitrary dimension, with no restrictions on the residue fields or characteristics.

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Automatically collected notes (unreviewed)

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

  • S. B. Iyengar, L. Ma, M. Walker, Lech's conjecture in equal characteristic (preliminary draft, 20 pp., posted on Walker's website, October 2026). A human-written account of a separate AI-generated proof of the equal-characteristic case (found by Alex Gerko with ChatGPT Astra), going through a Dutta-multiplicity lower bound $\chi_\infty(F)\ge e(R)$ in characteristic $p$ and a length bound for "deep" finite free resolutions inspired by Boij–Söderberg theory. This parallels this paper's uniform complex estimate and its Dutta corollary. [AI-generated per source]

Comments and discussion

Formalization

  • OpenAI math release, Lean scope note lean/docs/194.md (OpenAI Math Release, 2026-10-06). The formalization covers convergence of the Frobenius multiplicity sequence and the comparison $e(D)\le\chi_\infty(F)$ for short complexes over complete local domains of characteristic $p$. It does not cover the flat-local main theorem in arbitrary characteristic.
  • OpenAI math release, DuttaDomain.lean (theorem dutta_domain) (openai/math, 2026). The Lean proof file for the complete-domain Dutta comparison (statement in lean/ComparatorChallenges/DuttaDomain.lean), a 54-line file delegating to the auxiliary lemma dutta_complete_charp and importing OAI.RingTheory.Multiplicity.DuttaAlgClosed.

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

Elsewhere

Independent sites; their content is not reviewed here.

Cite

@misc{OAI:Lechs-multiplicity-conjecture-September-23-2026,
  author = {{OpenAI}},
  title = {{Lech's multiplicity conjecture}},
  howpublished = {OpenAI Math Release preprint
                  \href{https://github.com/openai/math/blob/main/preprints/Lechs-multiplicity-conjecture-September-23-2026/paper.pdf}{OAI:Lechs-multiplicity-conjecture-September-23-2026}},
  year = {2026}
}

Lean formalization

OpenAI provides Lean files for this family: lean/docs/194.md. The Lean statements have not been checked by people against the paper's claims.

Family 194: Lech’s multiplicity conjecture

Proves $e(R)\le e(S)$ for every flat local homomorphism of nonzero Noetherian local rings, where e is Hilbert–Samuel multiplicity. This resolves Lech's conjecture in every dimension and characteristic.

This is the only paper in this family.