The Bishop--Phelps--Bollobás property for Lipschitz maps

Rafael Chiclana, Miguel Martin

Published 2019-01-09Version 1

In this paper, we introduce and study a Lipschitz version of the Bishop-Phelps-Bollob\'as property (Lip-BPB property). This property deals with the possibility to make a uniformly simultaneous approximation of a Lipschitz map $F$ and a pair of points at which $F$ almost attains its norm by a Lipschitz map $G$ and a pair of points such that $G$ strongly attains its norm at the new pair of points. We first show that if $M$ is a finite pointed metric space and $Y$ is a finite-dimensional Banach space, then the pair $(M,Y)$ has the Lip-BPB property, and that both finiteness are needed. Next, we show that if $M$ is a uniformly Gromov concave pointed metric space (i.e.\ the molecules of $M$ form a set of uniformly strongly exposed points), then $(M,Y)$ has the Lip-BPB property for every Banach space $Y$. We further prove that this is the case of finite concave metric spaces, ultrametric spaces, and H\"older metric spaces. The extension of the Lip-BPB property from $(M,\mathbb{R})$ to some Banach spaces $Y$, the relationship with absolute sums, and some results only valid for compact Lipschitz maps, are also discussed.