A sofic group away from amenable groups
نویسندگان
چکیده
منابع مشابه
A Sofic Group Away from Amenable Groups
We give an example of a sofic group, which is not a limit of amenable groups.
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Throughout we let Γ be a discrete group. For f : Γ → C and each s ∈ Γ we define the left translation action by (s.f)(t) = f(s−1t). Definition 1.1. A group Γ is amenable is there exists a state μ on l∞(Γ) which is invariant under the left translation action: for all s ∈ Γ and f ∈ l∞(Γ), μ(s.f) = μ(f). Example 1.2. Finite groups are amenable: take the state which sends χ{s} to 1 |Γ| for each s ∈ ...
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This is an introductory survey of the emerging theory of two new classes of (discrete, countable) groups, called hyperlinear and sofic groups. They can be characterized as subgroups of metric ultraproducts of families of, respectively, unitary groups U(n) and symmetric groups Sn, n ∈ N. Hyperlinear groups come from theory of operator algebras (Connes’ Embedding Problem), while sofic groups, int...
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ژورنال
عنوان ژورنال: Mathematische Annalen
سال: 2010
ISSN: 0025-5831,1432-1807
DOI: 10.1007/s00208-010-0557-8