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Journals and Conferences
We study the composition operators on an algebra of Dirichlet series, the analogue of the Wiener algebra of absolutely convergent Taylor series, which we call the Wiener-Dirichlet algebra, namely the connection between the properties of the operator and of its symbol, with special emphasis on the compact, automorphic, or isometric character of this… (More)
We give a new vector-valued extension of DevilleGodefroy-Zizler perturbed minimization principle. The functions we are considering are taking values in a real Banach space partially ordered by a closed convex pointed cone. Mathematics Subject Classification. 46B20, 49N.
We study the numerical index of a Banach space from the isomorphic point of view, that is, we investigate the values of the numerical index which can be obtained by renorming the space. The set of these values is always an interval which contains [0, 1/3[ in the real case and [e−1, 1/2[ in the complex case. Moreover, for “most” Banach spaces the least upper… (More)
This paper is a short survey on the numerical range of some composition operators. The first part is devoted to composition operators on the Hilbert Hardy space H2 on the unit disk. The results are due to P. Bourdon, J. Shapiro and V. Matache. In the second part we study the numerical range of composition operators on the Hilbert space H 2 of Dirichlet… (More)
We prove that every M-ideal is strongly proximinal and that, for any Banach space X , K(X ,c0) is an M-ideal in L(X , ` ∞). Mathematics Subject Classification: 41A50, 41A65, 46B20.