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The exceptional sets for functions of the Bergman space in the unit ball

Piotr Jakóbczak (1993)

Atti della Accademia Nazionale dei Lincei. Classe di Scienze Fisiche, Matematiche e Naturali. Rendiconti Lincei. Matematica e Applicazioni

Let D be a domain in C 2 . Given w C , set D w = z C z , w D . If f is a holomorphic and square-integrable function in D , then the set E D , f of all w such that f ( , w ) is not square-integrable in D w has measure zero. We call this set the exceptional set for f . In this Note we prove that whenever 0 < r < 1 there exists a holomorphic square-integrable function f in the unit ball B in C 2 such that E B , f is the circle C 0 , r = z C z = r .

The Gleason-Kahane-Zelazko theorem and function algebras

Edoardo Vesentini (2005)

Atti della Accademia Nazionale dei Lincei. Classe di Scienze Fisiche, Matematiche e Naturali. Rendiconti Lincei. Matematica e Applicazioni

A theorem due to A. Gleason, J.-P. Kahane and W. Zelazko characterizes continuous characters within the space of all continuous linear forms of a locally multiplicatively convex, sequentially complete algebra. The present paper applies these results to investigate linear isometries of Banach algebras (with particular attention to normal uniform algebras) and of some locally multiplicatively convex algebras. The locally multiplicatively convex algebra of all holomorphic functions on a domain, will...

The kh-socle of a commutative semisimple Banach algebra

Youness Hadder (2020)

Mathematica Bohemica

Let 𝒜 be a commutative complex semisimple Banach algebra. Denote by kh ( soc ( 𝒜 ) ) the kernel of the hull of the socle of 𝒜 . In this work we give some new characterizations of this ideal in terms of minimal idempotents in 𝒜 . This allows us to show that a “result” from Riesz theory in commutative Banach algebras is not true.

The norm spectrum in certain classes of commutative Banach algebras

H. S. Mustafayev (2011)

Colloquium Mathematicae

Let A be a commutative Banach algebra and let Σ A be its structure space. The norm spectrum σ(f) of the functional f ∈ A* is defined by σ ( f ) = f · a : a A ¯ Σ A , where f·a is the functional on A defined by ⟨f·a,b⟩ = ⟨f,ab⟩, b ∈ A. We investigate basic properties of the norm spectrum in certain classes of commutative Banach algebras and present some applications.

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