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Manifold structure of the free Lie group Fr_

Determine whether the Polish group Fr_ = Fr ∩ Afr_ admits a structure of an infinite-dimensional manifold.

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Background

The paper constructs completions of the free associative algebra Afr_n with norms ||·||σ to form Banach algebras Afrσ and their inverse-limit Fréchet algebra Afr_. Corresponding completed free Lie algebras fr_σ and fr_∞ (denoted here by fr_) are defined, along with the groups Fr_σ = Fr_n ∩ Afr_σ and Fr_ = Fr_n ∩ Afr_. The groups Fr_σ are shown to be Banach-Lie groups, Polish, and contractible, with neighborhoods of the identity generated by the exponential map.

For Fr_ (the intersection over all σ>0), the paper proves Polishness, contractibility, and density of the subgroup generated by exponentials, but the author explicitly states uncertainty about whether Fr_ carries any standard infinite-dimensional manifold structure. Resolving this would clarify whether Fr_ fits within established frameworks of infinite-dimensional manifolds (e.g., Banach or Fréchet manifolds) used in infinite-dimensional Lie theory.

References

I do not know if Fr_ is an infinite-dimensional manifold in some formal sense.

A Lie group corresponding to the free Lie algebra and its universality (2411.11184 - Neretin, 17 Nov 2024) in Section 2.2, Remark (following Corollary 2.5)