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### 2-summing multiplication operators

Studia Mathematica

Let 1 ≤ p < ∞, $={\left(Xₙ\right)}_{n\in ℕ}$ be a sequence of Banach spaces and ${l}_{p}\left(\right)$ the coresponding vector valued sequence space. Let $={\left(Xₙ\right)}_{n\in ℕ}$, $={\left(Yₙ\right)}_{n\in ℕ}$ be two sequences of Banach spaces, $={\left(Vₙ\right)}_{n\in ℕ}$, Vₙ: Xₙ → Yₙ, a sequence of bounded linear operators and 1 ≤ p,q < ∞. We define the multiplication operator ${M}_{}:{l}_{p}\left(\right)\to {l}_{q}\left(\right)$ by ${M}_{}\left({\left(xₙ\right)}_{n\in ℕ}\right):={\left(Vₙ\left(xₙ\right)\right)}_{n\in ℕ}$. We give necessary and sufficient conditions for ${M}_{}$ to be 2-summing when (p,q) is one of the couples (1,2), (2,1), (2,2), (1,1), (p,1), (p,2), (2,p), (1,p), (p,q); in the last case 1 < p < 2, 1 < q < ∞.

### A note on embedding into product spaces

Czechoslovak Mathematical Journal

Using factorization properties of an operator ideal over a Banach space, it is shown how to embed a locally convex space from the corresponding Grothendieck space ideal into a suitable power of $E$, thus achieving a unified treatment of several embedding theorems involving certain classes of locally convex spaces.

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

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...

### An approximation property with respect to an operator ideal

Studia Mathematica

Given an operator ideal , we say that a Banach space X has the approximation property with respect to if T belongs to ${\overline{S\circ T:S\in ℱ\left(X\right)}}^{{\tau }_{c}}$ for every Banach space Y and every T ∈ (Y,X), ${\tau }_{c}$ being the topology of uniform convergence on compact sets. We present several characterizations of this type of approximation property. It is shown that some of the existing approximation properties in the literature may be included in this setting.

### Analytic multivalued functions and spectral trace.

Mathematische Annalen

### Arens-regularity of algebras arising from tensor norms.

The New York Journal of Mathematics [electronic only]

### Banach spaces with small Calkin algebras

Banach Center Publications

Let X be a Banach space. Let 𝓐(X) be a closed ideal in the algebra ℒ(X) of the operators acting on X. We say that ℒ(X)/𝓐(X) is a Calkin algebra whenever the Fredholm operators on X coincide with the operators whose class in ℒ(X)/𝓐(X) is invertible. Among other examples, we have the cases in which 𝓐(X) is the ideal of compact, strictly singular, strictly cosingular and inessential operators, and some other ideals introduced as perturbation classes in Fredholm theory. Our aim is to present some...

### Besov spaces and 2-summing operators

Colloquium Mathematicae

Let Π₂ be the operator ideal of all absolutely 2-summing operators and let ${I}_{m}$ be the identity map of the m-dimensional linear space. We first establish upper estimates for some mixing norms of ${I}_{m}$. Employing these estimates, we study the embedding operators between Besov function spaces as mixing operators. The result obtained is applied to give sufficient conditions under which certain kinds of integral operators, acting on a Besov function space, belong to Π₂; in this context, we also consider the...

### Can $ℬ\left({\ell }^{p}\right)$ ever be amenable?

Studia Mathematica

It is known that $ℬ\left({\ell }^{p}\right)$ is not amenable for p = 1,2,∞, but whether or not $ℬ\left({\ell }^{p}\right)$ is amenable for p ∈ (1,∞) ∖ 2 is an open problem. We show that, if $ℬ\left({\ell }^{p}\right)$ is amenable for p ∈ (1,∞), then so are ${\ell }^{\infty }\left(ℬ\left({\ell }^{p}\right)\right)$ and ${\ell }^{\infty }\left(\left({\ell }^{p}\right)\right)$. Moreover, if ${\ell }^{\infty }\left(\left({\ell }^{p}\right)\right)$ is amenable so is ${\ell }^{\infty }\left(,\left(E\right)\right)$ for any index set and for any infinite-dimensional ${ℒ}^{p}$-space E; in particular, if ${\ell }^{\infty }\left(\left({\ell }^{p}\right)\right)$ is amenable for p ∈ (1,∞), then so is ${\ell }^{\infty }\left(\left({\ell }^{p}\oplus \ell ²\right)\right)$. We show that ${\ell }^{\infty }\left(\left({\ell }^{p}\oplus \ell ²\right)\right)$ is not amenable for p = 1,∞, but also that our methods fail us if p ∈ (1,∞). Finally, for p ∈ (1,2) and a free ultrafilter over ℕ, we exhibit...

### Closed ideals in the Banach algebra of operators on a Banach space

Banach Center Publications

In general, little is known about the lattice of closed ideals in the Banach algebra ℬ(E) of all bounded, linear operators on a Banach space E. We list the (few) Banach spaces for which this lattice is completely understood, and we give a survey of partial results for a number of other Banach spaces. We then investigate the lattice of closed ideals in ℬ(F), where F is one of Figiel's reflexive Banach spaces not isomorphic to their Cartesian squares. Our main result is that this lattice is uncountable....

### Closed operator ideals and limiting real interpolation

Studia Mathematica

We establish interpolation properties under limiting real methods for a class of closed ideals including weakly compact operators, Banach-Saks operators, Rosenthal operators and Asplund operators. We show that they behave much better than compact operators.

### Complex rotundities and midpoint local uniform rotundity in symmetric spaces of measurable operators

Studia Mathematica

We investigate the relationships between strongly extreme, complex extreme, and complex locally uniformly rotund points of the unit ball of a symmetric function space or a symmetric sequence space E, and of the unit ball of the space E(ℳ,τ) of τ-measurable operators associated to a semifinite von Neumann algebra (ℳ,τ) or of the unit ball in the unitary matrix space ${C}_{E}$. We prove that strongly extreme, complex extreme, and complex locally uniformly rotund points x of the unit ball of the symmetric...

### Composition of (E,2)-summing operators

Studia Mathematica

The Banach operator ideal of (q,2)-summing operators plays a fundamental role within the theory of s-number and eigenvalue distribution of Riesz operators in Banach spaces. A key result in this context is a composition formula for such operators due to H. König, J. R. Retherford and N. Tomczak-Jaegermann. Based on abstract interpolation theory, we prove a variant of this result for (E,2)-summing operators, E a symmetric Banach sequence space.

### Compositions of operator ideals and their regular hulls

Acta Universitatis Carolinae. Mathematica et Physica

### Conical measures and properties of a vector measure determined by its range

Studia Mathematica

We characterize some properties of a vector measure in terms of its associated Kluvánek conical measure. These characterizations are used to prove that the range of a vector measure determines these properties. So we give new proofs of the fact that the range determines the total variation, the σ-finiteness of the variation and the Bochner derivability, and we show that it also determines the (p,q)-summing and p-nuclear norm of the integration operator. Finally, we show that Pettis derivability...

### Copies of ${l}_{p}^{n}$’s uniformly in the spaces ${\Pi }_{2}\left(C\left[0,1\right],X\right)$ and ${\Pi }_{1}\left(C\left[0,1\right],X\right)$

Czechoslovak Mathematical Journal

We study the presence of copies of ${l}_{p}^{n}$’s uniformly in the spaces ${\Pi }_{2}\left(C\left[0,1\right],X\right)$ and ${\Pi }_{1}\left(C\left[0,1\right],X\right)$. By using Dvoretzky’s theorem we deduce that if $X$ is an infinite-dimensional Banach space, then ${\Pi }_{2}\left(C\left[0,1\right],X\right)$ contains $\lambda \sqrt{2}$-uniformly copies of ${l}_{\infty }^{n}$’s and ${\Pi }_{1}\left(C\left[0,1\right],X\right)$ contains $\lambda$-uniformly copies of ${l}_{2}^{n}$’s for all $\lambda >1$. As an application, we show that if $X$ is an infinite-dimensional Banach space then the spaces ${\Pi }_{2}\left(C\left[0,1\right],X\right)$ and ${\Pi }_{1}\left(C\left[0,1\right],X\right)$ are distinct, extending the well-known result that the spaces ${\Pi }_{2}\left(C\left[0,1\right],X\right)$ and $𝒩\left(C\left[0,1\right],X\right)$ are distinct.

### Domination of operators in the non-commutative setting

Studia Mathematica

We consider majorization problems in the non-commutative setting. More specifically, suppose E and F are ordered normed spaces (not necessarily lattices), and 0 ≤ T ≤ S in B(E,F). If S belongs to a certain ideal (for instance, the ideal of compact or Dunford-Pettis operators), does it follow that T belongs to that ideal as well? We concentrate on the case when E and F are C*-algebras, preduals of von Neumann algebras, or non-commutative function spaces. In particular, we show that, for C*-algebras...

### Double Operator Integrals and Submajorization

Mathematical Modelling of Natural Phenomena

We present a user-friendly version of a double operator integration theory which still retains a capacity for many useful applications. Using recent results from the latter theory applied in noncommutative geometry, we derive applications to analogues of the classical Heinz inequality, a simplified proof of a famous inequality of Birman-Koplienko-Solomyak and also to the Connes-Moscovici inequality. Our methods are sufficiently strong to treat these...

### Dual results of factorization for operators.

Annales Academiae Scientiarum Fennicae. Series A I. Mathematica

### Duality of measures of non-𝒜-compactness

Studia Mathematica

Let be a Banach operator ideal. Based on the notion of -compactness in a Banach space due to Carl and Stephani, we deal with the notion of measure of non–compactness of an operator. We consider a map ${\chi }_{}$ (respectively, ${n}_{}$) acting on the operators of the surjective (respectively, injective) hull of such that ${\chi }_{}\left(T\right)=0$ (respectively, ${n}_{}\left(T\right)=0$) if and only if the operator T is -compact (respectively, injectively -compact). Under certain conditions on the ideal , we prove an equivalence inequality involving ${\chi }_{}\left(T*\right)$ and ${n}_{{}^{d}}\left(T\right)$....

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