Self-Induced Compactness in Banach Spaces

Abstract

The question which led to the title of this note is the following: {\it If $X$ is a Banach space and $K$ is a compact subset of $X$, is it possible to find a compact, or even approximable, operator $v:X\to X$ such that $K\subset\ol{v(B_X)}$?} This question was first posed by P.G.Dixon [6] in connection with investigating the problem of the existence of approximate identities in certain operator algebras. We shall provide a couple of observations related to the above question and give in particular a negative answer in case of approximable operators. We shall also provide the first examples of Banach spaces having the approximation property but failing the bounded compact approximation property though all of their duals do even have the metric compact approximation property.