Small combination of slices, dentability and stability results of small diameter properties in Banach spaces

Abstract

In this work we study three different versions of small diameter properties of the unit ball in a Banach space and its dual. The related concepts for all closed bounded convex sets of a Banach space was initiated and developed in [9], [4], [12], [13] was extensively studied in the context of dentability, huskability, Radon Nikodym Property and Krein Milman Property in [14]. We introduce the Ball Huskable Property (BHP), namely, the unit ball has relatively weakly open subsets of arbitrarily small diameter. We compare this property to two related properties, BSCSP namely, the unit ball has convex combination of slices of arbitrarily small diameter and BDP namely, the closed unit ball has slices of arbitrarily small diameter. We show BDP implies BHP which in turn implies BSCSP and none of the implications can be reversed. We prove similar results for the w⁎-versions. We prove that all these properties are stable under lp sum for 1≤p≤∞,c0 sum and Lebesgue Bochner spaces. Finally, we explore the stability of these with properties in the light of three space property. We show that BHP is a three space property provided X/Y is finite dimensional and same is true for BSCSP when X has BSCSP and X/Y is strongly regular ([14]).