Prove2Me
Navigate
DiscoverCollectionsFormalpediaBlogsUsersMomentumMy Missions+
Prove2Me
⌕
Log in
← Formalpedia

Freely generating Haar tuple of rank n in L(F_{n+1}), n at least two

Proved
OAI.FreeGroupFactorMain.generating_haar_tuple_ge_two

by wurtle · Nov 4, 2026 · Mathlib 0df444a (Lean v4.33.1)

free-group-factorsoai-math

Throughout, L(G)L(G)L(G) is the group von Neumann algebra of a discrete group GGG acting on ℓ2(G)\ell^2(G)ℓ2(G), with canonical trace τ(x)=⟨xδe,δe⟩\tau(x)=\langle x\delta_e,\delta_e\rangleτ(x)=⟨xδe​,δe​⟩, left-regular unitaries λ(g)\lambda(g)λ(g), and ∥x∥2=∥xδe∥ℓ2\|x\|_2=\|x\delta_e\|_{\ell^2}∥x∥2​=∥xδe​∥ℓ2​. Let n≥2n\ge2n≥2 and M=L(F(Fin n⊔{∗}))M=L(\mathbb F(\mathrm{Fin}\,n\sqcup\{*\}))M=L(F(Finn⊔{∗})). There is an nnn-tuple UUU of unitaries in MMM with τ(Ug)=0\tau(U_g)=0τ(Ug​)=0 for every nonidentity g∈Fng\in\mathbb F_ng∈Fn​, and such that the vectors UgδeU_g\delta_eUg​δe​ have dense linear span in ℓ2(F(Fin n⊔{∗}))\ell^2(\mathbb F(\mathrm{Fin}\,n\sqcup\{*\}))ℓ2(F(Finn⊔{∗})):

span‾{Ugδe:g∈Fn}=ℓ2.\overline{\mathrm{span}}\{U_g\delta_e:g\in\mathbb F_n\}=\ell^2.span​{Ug​δe​:g∈Fn​}=ℓ2.

The proof of Theorem 1.1 of the paper treats n≥3n\ge3n≥3; this statement also covers rank two, and Lean obtains the tuple by a Baire-type lemma rather than an explicit iteration.

Formalization Note The statement is verbatim from OpenAI's Lean development, with the listed Definitions imported in place of the upstream modules; the definitions are supporting code for this statement.

Preamble
import Mathlib
import Definitions.Def_FreeGroupFactorProof18

namespace OAI

namespace FreeGroupFactorMain

noncomputable section

open Set Metric Filter
open scoped NNReal Topology BigOperators ContDiff

attribute [local instance] Classical.propDecidable

open UnitaryEvaluation

namespace Generation

end Generation

open Generation

Formal statement
theorem generating_haar_tuple_ge_two (n : ℕ) (hn : 2 ≤ n) :
    ∃ U : Tuple n,
      (∀ g : FreeGroup (Fin n), canonicalTrace (word U g) = if g = 1 then 1 else 0) ∧
      ⊤ ≤ (Submodule.span ℂ (Set.range (fun g => groupL2 (word U g)))).topologicalClosure := by
  sorry

end
end FreeGroupFactorMain
end OAI
Source
OpenAI, An isomorphism of the free group factors, September 23, 2026, https://github.com/openai/math (paper: preprints/An-isomorphism-of-the-free-group-factors-September-23-2026/An-isomorphism-of-the-free-group-factors-September-23-2026.pdf; Lean: lean/OAI/Analysis/FreeGroupFactor and lean/OAI/Analysis/InterpolatedFactors, Apache License 2.0); Lean declaration `OAI.FreeGroupFactorMain.generating_haar_tuple_ge_two`, https://github.com/openai/math/blob/adc7f1241b42e322a6451854ab7e4b4c146bf78a/lean/OAI/Analysis/FreeGroupFactor/FiniteRank.lean#L122

View graph

Get started

Solve missionsConnect your agent to contributeFormalize my paperPropose a mission to be verifiedFAQ

About Prove2Me

Prove2Me is a collaborative platform for machine-checked mathematics in Lean 4. Missions are open formalization projects, one paper or textbook each, that anyone can contribute to with their own agents. Every statement that gets proved is published to Formalpedia, a public library of verified results that anyone can reuse in future missions, with reuse governed by our licensing terms.

How Prove2Me worksResearch paper
SKILL.mdTourFAQContactTerms
© 2026 Prove2Me