We shall show that every differential operator of 2-nd order in a real separable Hilbert space can be decomposed into a regular and an irregular operator. Then we shall characterize irregular operators and differential operators satisfying the maximum principle. Results obtained for the Lévy laplacian in [3] will be generalized for irregular differential operators satisfying the maximum principle.
A topological space (T,τ) is said to be fragmented by a metric d on T if each non-empty subset of T has non-empty relatively open subsets of arbitrarily small d-diameter. The basic theorem of the present paper is the following. Let (M,ϱ) be a metric space with ϱ bounded and let D be an arbitrary index set. Then for a compact subset K of the product space the following four conditions are equivalent: (i) K is fragmented by , where, for each S ⊂ D, . (ii) For each countable subset A of D, is...
A complete description of the real interpolation space is given. An interesting feature of the result is that the whole measure space (Ω,μ) can be divided into disjoint pieces (i ∈ I) such that L is an sum of the restrictions of L to , and L on each is a result of interpolation of just two weighted spaces. The proof is based on a generalization of some recent results of the first two authors concerning real interpolation of vector-valued spaces.
The main result of this paper states that if a Banach space X has the property that every bounded operator from an arbitrary subspace of X into an arbitrary Banach space of cotype 2 extends to a bounded operator on X, then every operator from X to an L₁-space factors through a Hilbert space, or equivalently . If in addition X has the Gaussian average property, then it is of type 2. This implies that the same conclusion holds if X has the Gordon-Lewis property (in particular X could be a Banach...
We show that every subspace of finite codimension of the space C[0,1] is extremal with respect to the minimal displacement problem.
In the theory of normed spaces, we have the concept of bounded linear functionals and dual spaces. Now, given an -normed space, we are interested in bounded multilinear -functionals and -dual spaces. The concept of bounded multilinear -functionals on an -normed space was initially intoduced by White (1969), and studied further by Batkunde et al., and Gozali et al. (2010). In this paper, we revisit the definition of bounded multilinear -functionals, introduce the concept of -dual spaces, and...
We study the numerical radius of Lipschitz operators on Banach spaces. We give its basic properties. Our main result is a characterization of finite-dimensional real Banach spaces with Lipschitz numerical index 1. We also explicitly compute the Lipschitz numerical index of some classical Banach spaces.