Christopher J. Lennard

arXiv1993

Every nonreflexive subspace of L_1[0,1] fails the fixed point property

The main result of this paper is that every non-reflexive subspace $Y$ of $L_1[0,1]$ fails the fixed point property for closed, bounded, convex subsets $C$ of $Y$ and nonexpansive (or contractive) mappings on $C$. Combined with a theorem of Maurey we get that for subspaces $Y$ of $L_1[0,1]$, $Y$ is reflexive if and only if $Y$ has the fixed point property. For general Banach spaces the question as to whether reflexivity implies the fixed point property and the converse question are both still open.

math.FA↗

arXiv1993

A Uniform Kadec-klee Property For Symmetric Operator Spaces

We show that if a rearrangement invariant Banach function space $E$ on the positive semi-axis satisfies a non-trivial lower $q-$ estimate with constant $1$ then the corresponding space $E(\nm)$ of $τ-$measurable operators, affiliated with an arbitrary semi-finite von Neumann algebra $\nm$ equipped with a distinguished faithful, normal, semi-finite trace $τ$, has the uniform Kadec-Klee property for the topology of local convergence in measure. In particular, the Lorentz function spaces $L_{q,p}$ and the Lorentz-Schatten classes ${\cal C}_{q,p}$ have the UKK property for convergence locally in measure and for the weak-operator topology, respectively. As a partial converse , we show that if $E$ has the UKK property with respect to local convergence in measure then $E$ must satisfy some non-trivial lower $q$-estimate. We also prove a uniform Kadec-Klee result for local convergence in any Banach lattice satisfying a lower $q$-estimate.

math.FA↗