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Erratum to “Tchebotaröv’s extremal problem”

Promarz Tamrazov (2009)

Open Mathematics

The original version of the article was published in Central European Journal of Mathematics, 2005, 3(4), 591–605. Unfortunately, the original version of this article contains a mistake. We give some corrections to our work.

Erratum to the paper "On the disc theorem" (Ann. Polon. Math. 55 (1991), 1-10)

Cabiria Andreian Cazacu (1992)

Annales Polonici Mathematici

Due to a technical error, part of a sentence was omitted on the top of page 8. The first line should read: “where f p k , p = a l or b l , means the number of folds of the covering ( δ k ' ' , T | , Δ l ' ' ) ending at p, i.e. covering a neighbourhood of p in a l b l without covering p itself”.

Essential norm of the difference of composition operators on Bloch space

Ke-Ben Yang, Ze-Hua Zhou (2010)

Czechoslovak Mathematical Journal

Let ϕ and ψ be holomorphic self-maps of the unit disk, and denote by C ϕ , C ψ the induced composition operators. This paper gives some simple estimates of the essential norm for the difference of composition operators C ϕ - C ψ from Bloch spaces to Bloch spaces in the unit disk. Compactness of the difference is also characterized.

Essential normality for certain finite linear combinations of linear-fractional composition operators on the Hardy space H 2

Mahsa Fatehi, Bahram Khani Robati (2012)

Czechoslovak Mathematical Journal

In 1999 Nina Zorboska and in 2003 P. S. Bourdon, D. Levi, S. K. Narayan and J. H. Shapiro investigated the essentially normal composition operator C ϕ , when ϕ is a linear-fractional self-map of 𝔻 . In this paper first, we investigate the essential normality problem for the operator T w C ϕ on the Hardy space H 2 , where w is a bounded measurable function on 𝔻 which is continuous at each point of F ( ϕ ) , ϕ 𝒮 ( 2 ) , and T w is the Toeplitz operator with symbol w . Then we use these results and characterize the essentially normal...

Essential norms of weighted composition operators on the space of Dirichlet series

Pascal Lefèvre (2009)

Studia Mathematica

We estimate the essential norm of a weighted composition operator relative to the class of Dunford-Pettis operators or the class of weakly compact operators, on the space of Dirichlet series. As particular cases, we obtain the precise value of the generalized essential norm of a composition operator and of a multiplication operator.

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