Freely generating Haar tuple of rank n in L(F_{n+1}), n at least two
ProvedOAI.FreeGroupFactorMain.generating_haar_tuple_ge_twofree-group-factorsoai-math
Throughout, is the group von Neumann algebra of a discrete group acting on , with canonical trace , left-regular unitaries , and . Let and . There is an -tuple of unitaries in with for every nonidentity , and such that the vectors have dense linear span in :
The proof of Theorem 1.1 of the paper treats ; 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