c0, l1 and l∞ in function spaces.
Calkin algebras for Banach spaces with finitely decomposable quotients
For a Banach space X such that all quotients only admit direct decompositions with a number of summands smaller than or equal to n, we show that every operator T on X can be identified with an n × n scalar matrix modulo the strictly cosingular operators SC(X). More precisely, we obtain an algebra isomorphism from the Calkin algebra L(X)/SC(X) onto a subalgebra of the algebra of n × n scalar matrices which is triangularizable when X is indecomposable. From this fact we get some information on the...
Caractérisations de sous-espaces normés de de dimension finie
Characteristic of convexity of Köthe function spaces.
Characteristic of convexity of Musielak-Orlicz function spaces equipped with the Luxemburg norm
In this paper we extend the result of [6] on the characteristic of convexity of Orlicz spaces to the more general case of Musielak-Orlicz spaces over a non-atomic measure space. Namely, the characteristic of convexity of these spaces is computed whenever the Musielak-Orlicz functions are strictly convex.
Characterization of intermediate values of the triangle inequality II
In [Mineno K., Nakamura Y., Ohwada T., Characterization of the intermediate values of the triangle inequality, Math. Inequal. Appl., 2012, 15(4), 1019–1035] there was established a norm inequality which characterizes all intermediate values of the triangle inequality, i.e. C n that satisfy 0 ≤ C n ≤ Σj=1n ‖x j‖ − ‖Σj=1n x j‖, x 1,...,x n ∈ X. Here we study when this norm inequality attains equality in strictly convex Banach spaces.
Characterization of normed linear spaces with generalized Mazur intersection property
Let 𝓐 be a compatible collection of bounded subsets in a normed linear space. We give a characterization of the following generalized Mazur intersection property: every closed convex set A ∈ 𝓐 is an intersection of balls.
Characterization of Strongly Exposed Points in General Köthe-Bochner Banach Spaces
We study strongly exposed points in general Köthe-Bochner Banach spaces X(E). We first give a characterization of strongly exposed points of the set of X-selections of a measurable multifunction Γ. We then apply this result to the study of strongly exposed points of the closed unit ball of X(E). Precisely we show that if an element f is a strongly exposed point of , then |f| is a strongly exposed point of and f(ω)/∥ f(ω)∥ is a strongly exposed point of for μ-almost all ω ∈ S(f).
Characterization of the strict convexity of the Besicovitch-Musielak-Orlicz space of almost periodic functions
We introduce the new class of Besicovitch-Musielak-Orlicz almost periodic functions and consider its strict convexity with respect to the Luxemburg norm.
Characterization of weak type by the entropy distribution of r-nuclear operators
The dual of a Banach space X is of weak type p if and only if the entropy numbers of an r-nuclear operator with values in a Banach space of weak type q belong to the Lorentz sequence space with 1/s + 1/p + 1/q = 1 + 1/r (0 < r < 1, 1 ≤ p, q ≤ 2). It is enough to test this for Y = X*. This extends results of Carl, König and Kühn.
Characterizations of inner product structures involving the radius of the inscribed or circumscribed circumference
We define the radius of the inscribed and circumscribed circumferences in a triangle located in a real normed space and we obtain new characterizations of inner product spaces.
Characterizations of -predual spaces by centerable subsets
In this note, we prove that a real or complex Banach space is an -predual space if and only if every four-point subset of is centerable. The real case sharpens Rao’s result in [Chebyshev centers and centerable sets, Proc. Amer. Math. Soc. 130 (2002), no. 9, 2593–2598] and the complex case is closely related to the characterizations of -predual spaces by Lima [Complex Banach spaces whose duals are -spaces, Israel J. Math. 24 (1976), no. 1, 59–72].
Characterizations of reduced polytopes in finite-dimensional normed spaces.
Characterizations of spreading models of
Rosenthal in [11] proved that if is a uniformly bounded sequence of real-valued functions which has no pointwise converging subsequence then has a subsequence which is equivalent to the unit basis of in the supremum norm. Kechris and Louveau in [6] classified the pointwise convergent sequences of continuous real-valued functions, which are defined on a compact metric space, by the aid of a countable ordinal index “”. In this paper we prove some local analogues of the above Rosenthal ’s theorem...
Chebyshev centers, E-Chebyshev centers and the Hausdorff metric.
Chebyshev centers in hyperplanes of
We give a full characterization of the closed one-codimensional subspaces of , in which every bounded set has a Chebyshev center. It turns out that one can consider equivalently only finite sets (even only three-point sets) in our case, but not in general. Such hyperplanes are exactly those which are either proximinal or norm-one complemented.
Chebyshev coficients for L1-preduals and for spaces with the extension property.
We apply the Chebyshev coefficients λf and λb, recently introduced by the authors, to obtain some results related to certain geometric properties of Banach spaces. We prove that a real normed space E is an L1-predual if and only if λf(E) = 1/2, and that if a (real or complex) normed space E is a P1 space, then λb(E) equals λb(K), where K is the ground field of E.
Circumcenters in real normed spaces
The study of circumcenters in different types of triangles in real normed spaces gives new characterizations of inner product spaces.
Clarkson type inequalities and their relations to the concepts of type and cotype.
We prove some multi-dimensional Clarkson type inequalities for Banach spaces. The exact relations between such inequalities and the concepts of type and cotype are shown, which gives a conclusion in an extended setting to M. Milman's observation on Clarkson's inequalities and type. A similar investigation conceming the close connection between random Clarkson inequality and the corresponding concepts of type and cotype is also included. The obtained results complement, unify and generalize several...
Classes of nonseparable Banach spaces with no universal element