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A counterexample in operator theory

Antonio Córdoba (1993)

Publicacions Matemàtiques

The purpose of this note is to give an explicit construction of a bounded operator T acting on the space L2[0,1] such that |Tf(x)| ≤ ∫01 |f(y)| dy for a.e. x ∈ [0.1], and, nevertheless, ||T||Sp = ∞ for every p < 2. Here || ||Sp denotes the norm associated to the Schatten-Von Neumann classes.

A remark on the range of elementary operators

Said Bouali, Youssef Bouhafsi (2010)

Czechoslovak Mathematical Journal

Let L ( H ) denote the algebra of all bounded linear operators on a separable infinite dimensional complex Hilbert space H into itself. Given A L ( H ) , we define the elementary operator Δ A : L ( H ) L ( H ) by Δ A ( X ) = A X A - X . In this paper we study the class of operators A L ( H ) which have the following property: A T A = T implies A T * A = T * for all trace class operators T C 1 ( H ) . Such operators are termed generalized quasi-adjoints. The main result is the equivalence between this character and the fact that the ultraweak closure of the range of Δ A is closed under taking...

A unified approach to the strong approximation property and the weak bounded approximation property of Banach spaces

Aleksei Lissitsin (2012)

Studia Mathematica

We consider convex versions of the strong approximation property and the weak bounded approximation property and develop a unified approach to their treatment introducing the inner and outer Λ-bounded approximation properties for a pair consisting of an operator ideal and a space ideal. We characterize this type of properties in a general setting and, using the isometric DFJP-factorization of operator ideals, provide a range of examples for this characterization, eventually answering a question...

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