A note on nonfragmentability of Banach spaces.
A note on nonseparable Lipschitz-free spaces
We prove that several classical Banach space properties are equivalent to separability for the class of Lipschitz-free spaces, including Corson’s property (), Talponen’s countable separation property, or being a Gâteaux differentiability space. On the other hand, we single out more general properties where this equivalence fails. In particular, the question whether the duals of nonseparable Lipschitz-free spaces have a weak sequentially compact ball is undecidable in ZFC. Finally, we provide an...
A note on norm-attaining functionals
A note on Picard iterates of nonexpansive mappings
Let X be a Banach space, C a closed subset of X, and T:C → C a nonexpansive mapping. It has recently been shown that if X is reflexive and locally uniformly convex and if the fixed point set F(T) of T has nonempty interior then the Picard iterates of the mapping T always converge to a point of F(T). In this paper it is shown that if T is assumed to be asymptotically regular, this condition can be weakened much further. Finally, some observations are made about the geometric conditions imposed.
A Note on Preserved Smoothness
* Supported by NSERC (Canada)Let X be a Banach space equipped with norm || · ||. We say that || · || is Gâteaux differentiable at x if for every h ∈ SX(|| · ||), (∗) lim t→0 (||x + th|| − ||x||) / t exists. We say that the norm || · || is Gâteaux differentiable if || · || is Gâteaux differentiable at all x ∈ SX(|| · ||).
A note on properties that imply the fixed point property.
A Note on Remotal Sets in Banach Spaces
A note on rotation in separable Banach spaces
A note on Schroeder-Bernstein Property and Primary Property of Orlicz function spaces
It is shown in the note that every reflexive Orlicz function space has the Schroeder-Bernstein Property and the Primary Property.
A note on self-extremal sets in spaces.
A note on the class of superreflexive almost transitive Banach spaces.
A note on the Hyers-Ulam problem
Let X,Y be real Banach spaces and ε > 0. Suppose that f:X → Y is a surjective map satisfying | ∥f(x)-f(y)∥ - ∥x-y∥ | ≤ ε for all x,y ∈ X. Hyers and Ulam asked whether there exists an isometry U and a constant K such that ∥f(x) - Ux∥ ≤ Kε for all x ∈ X. It is well-known that the answer to the Hyers-Ulam problem is positive and K = 2 is the best possible solution with assumption f(0) = U0 = 0. In this paper, using the idea of Figiel's theorem on nonsurjective isometries, we give a new proof of...
A note on the modulus of -convexity and modulus of -convexity.
A note on the predual of Lip(S, d)
A note on the structure of WUR Banach spaces
We present an example of a Banach space admitting an equivalent weakly uniformly rotund norm and such that there is no , for any set , linear, one-to-one and bounded. This answers a problem posed by Fabian, Godefroy, Hájek and Zizler. The space is actually the dual space of a space which is a subspace of a WCG space.
A note on Tsirelson type ideals
Using Tsirelson’s well-known example of a Banach space which does not contain a copy of or , for p ≥ 1, we construct a simple Borel ideal such that the Borel cardinalities of the quotient spaces and are incomparable, where is the summable ideal of all sets A ⊆ ℕ such that . This disproves a “trichotomy” conjecture for Borel ideals proposed by Kechris and Mazur.
A note on weakly Lindelöf determined Banach spaces
We prove that weakly Lindelöf determined Banach spaces are characterized by the existence of a ``full'' projectional generator. Some other results pertaining to this class of Banach spaces are given.
A Pythagorean approach in Banach spaces.
A remark on polynomial norms and their coefficients.
A renorming of , rare but with the fixed-point property.