Twisted sums and a problem of Klee

Abstract

Let F be a quasi-linear map on a separable normed space X, and assume that F splits on an infinite-dimensional subspace of X. Then the twisted sum topology induced by F on the direct sum of X and the real line can be written as the supremum of a nearly convex topology and a trivial dual topology. (This partially answers a question of Klee.) The result applies when X is \ell_1 and F is the Ribe function or when X is James's space.