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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 class of Banach sequence spaces analogous to the space of Popov

Czechoslovak Mathematical Journal

Hagler and the first named author introduced a class of hereditarily ${l}_{1}$ Banach spaces which do not possess the Schur property. Then the first author extended these spaces to a class of hereditarily ${l}_{p}$ Banach spaces for $1\le p<\infty$. Here we use these spaces to introduce a new class of hereditarily ${l}_{p}\left({c}_{0}\right)$ Banach spaces analogous of the space of Popov. In particular, for $p=1$ the spaces are further examples of hereditarily ${l}_{1}$ Banach spaces failing the Schur property.

### A disjointness type property of conditional expectation operators

Colloquium Mathematicae

We give a characterization of conditional expectation operators through a disjointness type property similar to band-preserving operators. We say that the operator T:X→ X on a Banach lattice X is semi-band-preserving if and only if for all f, g ∈ X, f ⊥ Tg implies that Tf ⊥ Tg. We prove that when X is a purely atomic Banach lattice, then an operator T on X is a weighted conditional expectation operator if and only if T is semi-band-preserving.

### A Natural Class of Sequential Banach Spaces

Bulletin of the Polish Academy of Sciences. Mathematics

We introduce and study a natural class of variable exponent ${\ell }^{p}$ spaces, which generalizes the classical spaces ${\ell }^{p}$ and c₀. These spaces will typically not be rearrangement-invariant but instead they enjoy a good local control of some geometric properties. Some geometric examples are constructed by using these spaces.

### A note on continuous restrictions of linear maps between Banach spaces.

Acta Mathematica Universitatis Comenianae. New Series

### About the Banach envelope of l1,∞.

Revista Matemática Complutense

### Acción dual de las copias, isométricas asintóticamente, de lp (1 ≤ p &lt; ∞) y c0.

Collectanea Mathematica

### Algebraic and topological properties of some sets in ℓ₁

Colloquium Mathematicae

For a sequence x ∈ ℓ₁∖c₀₀, one can consider the set E(x) of all subsums of the series ${\sum }_{n=1}^{\infty }x\left(n\right)$. Guthrie and Nymann proved that E(x) is one of the following types of sets: () a finite union of closed intervals; () homeomorphic to the Cantor set; homeomorphic to the set T of subsums of ${\sum }_{n=1}^{\infty }b\left(n\right)$ where b(2n-1) = 3/4ⁿ and b(2n) = 2/4ⁿ. Denote by ℐ, and the sets of all sequences x ∈ ℓ₁∖c₀₀ such that E(x) has the property (ℐ), () and ( ), respectively. We show that ℐ and are strongly -algebrable and is -lineable. We...

### Amenability for discrete convolution semigroup algebras.

Mathematica Scandinavica

### An amalgamation of the Banach spaces associated with James and Schreier, Part I: Banach-space structure

Banach Center Publications

We create a new family of Banach spaces, the James-Schreier spaces, by amalgamating two important classical Banach spaces: James' quasi-reflexive Banach space on the one hand and Schreier's Banach space giving a counterexample to the Banach-Saks property on the other. We then investigate the properties of these James-Schreier spaces, paying particular attention to how key properties of their 'ancestors' (that is, the James space and the Schreier space) are expressed in them. Our main results include...

### An amalgamation of the Banach spaces associated with James and Schreier, Part II: Banach-algebra structure

Banach Center Publications

The James-Schreier spaces, defined by amalgamating James' quasi-reflexive Banach spaces and Schreier space, can be equipped with a Banach-algebra structure. We answer some questions relating to their cohomology and ideal structure, and investigate the relations between them. In particular we show that the James-Schreier algebras are weakly amenable but not amenable, and relate these algebras to their multiplier algebras and biduals.

### Approximation problems in modular spaces of double sequences.

Publicacions Matemàtiques

Let X denote the space of all real, bounded double sequences, and let Φ, φ, Γ be φ-functions. Moreover, let Ψ be an increasing, continuous function for u ≥ 0 such that Ψ(0) = 0.In this paper we consider some spaces of double sequences provided with two-modular structure given by generalized variations and the translation operator (...).

### Asymptotic uniform moduli and Kottman constant of Orlicz sequence spaces.

Revista Matemática Complutense

### Banach-Saks property in some Banach sequence spaces

Annales Polonici Mathematici

It is proved that for any Banach space X property (β) defined by Rolewicz in  implies that both X and X* have the Banach-Saks property. Moreover, in Musielak-Orlicz sequence spaces, criteria for the Banach-Saks property, the near uniform convexity, the uniform Kadec-Klee property and property (H) are given.

### Bicontractive projections in sequence spaces and a few related kinds of maps

Commentationes Mathematicae Universitatis Carolinae

### Boundedness and compactness of some operators on discrete Morrey spaces

Commentationes Mathematicae Universitatis Carolinae

We consider discrete versions of Morrey spaces introduced by Gunawan et al. in papers published in 2018 and 2019. We prove continuity and compactness of multiplication operators and commutators acting on them.

### Bounding Subsets of a Banach Space.

Mathematische Annalen

### Brèves communications. Comparaison de suites convergentes

ESAIM: Mathematical Modelling and Numerical Analysis - Modélisation Mathématique et Analyse Numérique

### 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...

### Cantor-Bernstein theorems for Orlicz sequence spaces

Banach Center Publications

For two Banach spaces X and Y, we write $di{m}_{\ell }\left(X\right)=di{m}_{\ell }\left(Y\right)$ if X embeds into Y and vice versa; then we say that X and Y have the same linear dimension. In this paper, we consider classes of Banach spaces with symmetric bases. We say that such a class ℱ has the Cantor-Bernstein property if for every X,Y ∈ ℱ the condition $di{m}_{\ell }\left(X\right)=di{m}_{\ell }\left(Y\right)$ implies the respective bases (of X and Y) are equivalent, and hence the spaces X and Y are isomorphic. We prove (Theorems 3.1, 3.3, 3.5) that the class of Orlicz sequence spaces generated by regularly...

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