Continuous Position and Existence Sets.
Convergence of convex functions and generalized inf-convolutive approximations. (Convergences des fonctions convexes et approximations inf-convolutives généralisées.)
Convergence of the dual greedy algorithm in Banach spaces.
Convex functions with non-Borel set of Gâteaux differentiability points
We show that on every nonseparable Banach space which has a fundamental system (e.gȯn every nonseparable weakly compactly generated space, in particular on every nonseparable Hilbert space) there is a convex continuous function such that the set of its Gâteaux differentiability points is not Borel. Thereby we answer a question of J. Rainwater (1990) and extend, in the same time, a former result of M. Talagrand (1979), who gave an example of such a function on .
Convex sets in Banach spaces and a problem of Rolewicz
Let be the set of all closed, convex and bounded subsets of a Banach space X equipped with the Hausdorff metric. In the first part of this work we study the density character of and investigate its connections with the geometry of the space, in particular with a property shared by the spaces of Shelah and Kunen. In the second part we are concerned with the problem of Rolewicz, namely the existence of support sets, for the case of spaces C(K).
Convexités uniformes et inégalités de martingales.
Convexity and Reflexivity
Convexity around the Unit of a Banach Algebra
2000 Mathematics Subject Classification: Primary: 46B20. Secondary: 46H99, 47A12.We estimate the (midpoint) modulus of convexity at the unit 1 of a Banach algebra A showing that inf {max±||1 ± x|| − 1 : x ∈ A, ||x||=ε} ≥ (π/4e)ε²+o(ε²) as ε → 0. We also give a characterization of two-dimensional subspaces of Banach algebras containing the identity in terms of polynomial inequalities.
Convexity, type and three space problem
Copies of and in Musielak-Orlicz sequence spaces
Criteria in order that a Musielak-Orlicz sequence space contains an isomorphic as well as an isomorphically isometric copy of are given. Moreover, it is proved that if , where are defined on a Banach space, does not satisfy the -condition, then the Musielak-Orlicz sequence space of -valued sequences contains an almost isometric copy of . In the case of it is proved also that if contains an isomorphic copy of , then does not satisfy the -condition. These results extend some...
Correction to “Domains of attraction in several dimensions”
Correction to the paper: Support functionals and smoothness in Musielak-Orlicz sequence spaces endowed with the Luxemburg norm
Corrigendum to “Commutators on ” (Studia Math. 206 (2011), 175-190)
We give a corrected proof of Theorem 2.10 in our paper “Commutators on ” [Studia Math. 206 (2011), 175-190] for the case 1 < q < p < ∞. The case when 1 = q < p < ∞ remains open. As a consequence, the Main Theorem and Corollary 2.17 in that paper are only valid for 1 < p,q < ∞.
Cotype and (q, 1)-summing norm in a Banach space.
Cotype for p-Banach spaces
Cotype of operators from C(K).
Countably convex sets
We investigate countably convex subsets of Banach spaces. A subset of a linear space is countably convex if it can be represented as a countable union of convex sets. A known sufficient condition for countable convexity of an arbitrary subset of a separable normed space is that it does not contain a semi-clique [9]. A semi-clique in a set S is a subset P ⊆ S so that for every x ∈ P and open neighborhood u of x there exists a finite set X ⊆ P ∩ u such that conv(X) ⊈ S. For closed sets this condition...
Criteria for in Musielak-Orlicz spaces
In this paper, some necessary and sufficient conditions for in Musielak-Orlicz function spaces as well as in Musielak-Orlicz sequence spaces are given.
Daugavet centers and direct sums of Banach spaces
A linear continuous nonzero operator G: X → Y is a Daugavet center if every rank-1 operator T: X → Y satisfies ||G + T|| = ||G|| + ||T||. We study the case when either X or Y is a sum X 1⊕F X 2 of two Banach spaces X 1 and X 2 by some two-dimensional Banach space F. We completely describe the class of those F such that for some spaces X 1 and X 2 there exists a Daugavet center acting from X 1⊕F X 2, and the class of those F such that for some pair of spaces X 1 and X 2 there is a Daugavet center...
De la recherche pétrolière à la géométrie des espaces de Banach en passant par les paraproduits