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Compact endomorphisms of H ( D )

Joel FeinsteinHerbert Kamowitz — 1999

Studia Mathematica

Compact composition operators on H ( G ) , where G is a region in the complex plane, and the spectra of these operators were described by D. Swanton ( Compact composition operators on B(D), Proc. Amer. Math. Soc. 56 (1976), 152-156). In this short note we characterize all compact endomorphisms, not necessarily those induced by composition operators, on H ( D ) , where D is the unit disc, and determine their spectra.

Completions of normed algebras of differentiable functions

William J. BlandJoel F. Feinstein — 2005

Studia Mathematica

We look at normed spaces of differentiable functions on compact plane sets, including the spaces of infinitely differentiable functions considered by Dales and Davie in [7]. For many compact plane sets the classical definitions give rise to incomplete spaces. We introduce an alternative definition of differentiability which allows us to describe the completions of these spaces. We also consider some associated problems of polynomial and rational approximation.

Quasicompact endomorphisms of commutative semiprime Banach algebras

Joel F. FeinsteinHerbert Kamowitz — 2010

Banach Center Publications

This paper is a continuation of our study of compact, power compact, Riesz, and quasicompact endomorphisms of commutative Banach algebras. Previously it has been shown that if B is a unital commutative semisimple Banach algebra with connected character space, and T is a unital endomorphism of B, then T is quasicompact if and only if the operators Tⁿ converge in operator norm to a rank-one unital endomorphism of B. In this note the discussion is extended in two ways: we discuss endomorphisms of commutative...

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