Lech's multiplicity conjectureOpen Problem
Motivation
Multiplicity measures the growth of infinitesimal neighborhoods in a local ring. The manuscript addresses Lech’s flat-local-map inequality; the available formal target isolates its complete-domain Frobenius-complex component. The source is OpenAI's September 2026 manuscript.
Setting
For a local domain of dimension , Hilbert–Samuel multiplicity is the limit of . A short complex has finite free terms in degrees through zero, finite-length homology, and nonzero zeroth homology. Its Frobenius scalar extensions define a normalized Euler-characteristic sequence.
Formalization targets
The defined proposition DuttaDomainClaim holds, in universe u. That claim says: let D be a commutative Noetherian local domain (in universe u) that is complete in the adic topology of its maximal ideal, with prime characteristic p, and let F be a cochain complex of D-modules indexed by the integers that is a short complex. Short means every term F^i is free and finitely generated, F^i is zero whenever i < -dim D or i > 0, every homology module of F has finite length, and the homology of F in degree 0 is nonzero. Here dim is the Krull dimension (taken as 0 if it is the bottom value). Let F_n denote F after extending scalars along the n-fold iterate of the Frobenius map of D. The conclusion has three parts. First, every homology module of every F_n has finite length. Second, the sequence a_n = p^(-n dim D) * chi(F_n) converges as n tends to infinity, where chi(G) is the alternating sum, over i from 0 to dim D, of (-1)^i times the length of the homology of G in degree -i; this limit is the Dutta multiplicity of F. Third, the Hilbert-Samuel multiplicity of D, defined as the limit of (dim D)! times the length of D/m^N divided by N^(dim D) as N tends to infinity, is at most the Dutta multiplicity of F.
The goal is OAI.Lech.dutta_domain.
Significance
The goal formalizes the lower bound by Dutta multiplicity together with the convergence and finite-length statements needed to interpret it. This is a precise component of the paper’s multiplicity program. The manuscript presents a mathematical argument; the attached goal currently has status Open, so the requested contribution is a Lean proof of the displayed formal target.
Difficulty
Lengths of homology after Frobenius extension must be controlled before normalized Euler characteristics can be used. A definition by a chosen limit does not by itself establish convergence.
Formalization scope
The ring is a complete Noetherian local domain in prime characteristic. The goal is DuttaDomainClaim, not the unrestricted flat local homomorphism inequality. Dimensions and lengths use the natural-number conversions in the supplied definitions, and convergence is an explicit conclusion.
The shared definitions are supplied by DuttaDomain. The target uses Lean 4.33.1 with the pinned Mathlib environment. Contributions should preserve the existing statement and develop reusable supporting lemmas in its definitions.
Selected references
- OpenAI, Lech's multiplicity conjecture, preprint, September 2026. Manuscript.
- OpenAI, accompanying Lean statement. Pinned source.