32 research outputs found

    Uniform algebras and approximation on manifolds

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    Let Ω⊂Cn\Omega \subset \mathbb{C}^n be a bounded domain and let A⊂C(Ωˉ)\mathcal{A} \subset \mathcal{C}(\bar{\Omega}) be a uniform algebra generated by a set FF of holomorphic and pluriharmonic functions. Under natural assumptions on Ω\Omega and FF we show that the only obstruction to A=C(Ωˉ)\mathcal{A} = \mathcal{C}(\bar{\Omega}) is that there is a holomorphic disk D⊂ΩˉD \subset \bar{\Omega} such that all functions in FF are holomorphic on DD, i.e., the only obstruction is the obvious one. This generalizes work by A. Izzo. We also have a generalization of Wermer's maximality theorem to the (distinguished boundary of the) bidisk

    Norm compactness of representing measures for R(K)

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    Perturbations of Unbounded Fredholm Linear Operators in Banach Spaces

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    A Stone-Weierstrass theorem for weak-star approximation by rational functions

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    AbstractLet K be a compact subset of the complex plane C, and let μ be a finite, positive Borel measure on K. Define R∞(μ) to be the weak-star closure in L∞(μ) of the algebra of rational functions with poles off K. For f ϵ R∞(μ), we consider A∞(f, μ), the weak-star closure in L∞(μ) of the algebra generated by R∞(μ) and the complex conjugate f of f. A problem which arises in connection with subnormal operators is to determine for which f ϵ R∞(μ), A∞(f, μ) = L∞(μ). We obtain a characterization of A∞(f,μ) as precisely the functions in L∞(μ) which belong to R∞(μE) for every restriction of μ to a level set E of f of positive measure. This characterization gives a solution to the problem above
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