2001
DOI: 10.1112/plms/82.3.676
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Factorization in finite-codimensional ideals of group algebras

Abstract: Let G be a σ‐compact, locally compact group and I be a closed 2‐sided ideal with finite codimension in L1(G). It is shown that there are a closed left ideal L having a right bounded approximate identity and a closed right ideal R having a left bounded approximate identity such that I = L + R. The proof uses ideas from the theory of boundaries of random walks on groups. 2000 Mathematics Subject Classification: primary 43A20; secondary 42A85, 43A07, 46H10, 46H40, 60B11.

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Cited by 7 publications
(6 citation statements)
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References 26 publications
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“…J µ is evidently a left ideal in the group algebra L 1 (G), whose annihilator in L ∞ (G) is precisely the space H µ of the bounded µ-harmonic functions. As pointed out by Willis [42,43], ideals of this form appear naturally not only in the theory of µ-harmonic functions but also in the study of amenability and certain factorization questions in group algebras. The quotient L 1 (G)/J µ turns out to be an abstract L 1 -space whose pointwise realization is the boundary needed to represent the µ-harmonic functions by means of a Poisson formula.…”
Section: The Preannihilator Of H µπmentioning
confidence: 99%
“…J µ is evidently a left ideal in the group algebra L 1 (G), whose annihilator in L ∞ (G) is precisely the space H µ of the bounded µ-harmonic functions. As pointed out by Willis [42,43], ideals of this form appear naturally not only in the theory of µ-harmonic functions but also in the study of amenability and certain factorization questions in group algebras. The quotient L 1 (G)/J µ turns out to be an abstract L 1 -space whose pointwise realization is the boundary needed to represent the µ-harmonic functions by means of a Poisson formula.…”
Section: The Preannihilator Of H µπmentioning
confidence: 99%
“…In the case where G is amenable, the ideal I has a BAI, and so factors. It is proved in [37] that I always factors weakly, even when it does not have a BAI. For example, let F 2 be the free group on two generators.…”
Section: Trivially (Iv)⇒(v)mentioning
confidence: 99%
“…These ideals, which have also been studied by G. Willis in a Banach algebra context (see e.g. [41]), for us correspond to the noncommutative variant of peak sets from the theory of function algebras (see [9,Proposition 6.7] for the correspondence). Here and in the following we write 1 for the identity in A 1 if A is a nonunital algebra.…”
Section: Existence Of R-idealsmentioning
confidence: 99%