Mapping in normed linear spaces and characterization of orthogonality problem of best approximations in 2-norm.
Metric criteria for Banach and Euclidean spaces
Mielnik's Probability Spaces and Characterization of Inner Product Spaces
Multiple summing operators on spaces
We use the Maurey-Rosenthal factorization theorem to obtain a new characterization of multiple 2-summing operators on a product of spaces. This characterization is used to show that multiple s-summing operators on a product of spaces with values in a Hilbert space are characterized by the boundedness of a natural multilinear functional (1 ≤ s ≤ 2). We use these results to show that there exist many natural multiple s-summing operators such that none of the associated linear operators is s-summing...