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An ideal characterization of when a subspace of certain Banach spaces has the metric compact approximation property

J. Cabello, E. Nieto (1998)

Studia Mathematica

C.-M. Cho and W. B. Johnson showed that if a subspace E of p , 1 < p < ∞, has the compact approximation property, then K(E) is an M-ideal in ℒ(E). We prove that for every r,s ∈ ]0,1] with r 2 + s 2 < 1 , the James space can be provided with an equivalent norm such that an arbitrary subspace E has the metric compact approximation property iff there is a norm one projection P on ℒ(E)* with Ker P = K(E)⊥ satisfying ∥⨍∥ ≥ r∥Pf∥ + s∥φ - Pf∥ ∀⨍ ∈ ℒ(E)*. A similar result is proved for subspaces of upper p-spaces...

An indecomposable and unconditionally saturated Banach space

Spiros A. Argyros, Antonis Manoussakis (2003)

Studia Mathematica

We construct an indecomposable reflexive Banach space X i u s such that every infinite-dimensional closed subspace contains an unconditional basic sequence. We also show that every operator T ( X i u s ) is of the form λI + S with S a strictly singular operator.

An indecomposable Banach space of continuous functions which has small density

Rogério Augusto dos Santos Fajardo (2009)

Fundamenta Mathematicae

Using the method of forcing we construct a model for ZFC where CH does not hold and where there exists a connected compact topological space K of weight ω < 2 ω such that every operator on the Banach space of continuous functions on K is multiplication by a continuous function plus a weakly compact operator. In particular, the Banach space of continuous functions on K is indecomposable.

An index formula for chains

Robin Harte, Woo Lee (1995)

Studia Mathematica

We derive a formula for the index of Fredholm chains on normed spaces.

An inequality between the James and James type constants in Banach spaces

Fenghui Wang, Changsen Yang (2010)

Studia Mathematica

We consider the James and Schäffer type constants recently introduced by Takahashi. We prove an equality between James (resp. Schäffer) type constants and the modulus of convexity (resp. smoothness). By using these equalities, we obtain some estimates for the new constants in terms of the James constant. As a result, we improve an inequality between the Zbăganu and James constants.

An inequality in Orlicz function spaces with Orlicz norm

Jin Cai Wang (2003)

Commentationes Mathematicae Universitatis Carolinae

We use Simonenko quantitative indices of an 𝒩 -function Φ to estimate two parameters q Φ and Q Φ in Orlicz function spaces L Φ [ 0 , ) with Orlicz norm, and get the following inequality: B Φ B Φ - 1 q Φ Q Φ A Φ A φ - 1 , where A Φ and B Φ are Simonenko indices. A similar inequality is obtained in L Φ [ 0 , 1 ] with Orlicz norm.

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