Lipschitz retractions and complementation properties of Banach spaces

TL;DR

This paper explores Lipschitz retraction structures in metric spaces, linking them to Banach space properties, and provides examples illustrating the limitations of Lipschitz retracts in certain metric spaces.

Contribution

It introduces the Lipschitz retractional structure in metric spaces, connects it to Banach space theory, and presents new examples and metric analogues of classical linear concepts.

Findings

Lipschitz free space of a Plichko Banach space is Plichko.

Constructed metric spaces with specific Lipschitz retraction properties.

Established metric analogues of locally complemented subspaces.

Abstract

In the present paper we introduce and study the Lipschitz retractional structure of metric spaces. This topic was motivated by the analogous projectional structure of Banach spaces, a topic that has been thoroughly investigated. The more general metric setting fits well with the currently active theory of Lipschitz free spaces and spaces of Lipschitz functions. Among our applications we show that the Lipschitz free space $\mathcal{F}(X)$ is a Plichko space whenever $X$ is a Plichko Banach space. Our main results include two examples of metric spaces. The first one $M$ contains two points $\{0,1\}$ such that no separable subset of $M$ containing these points is a Lipschitz retract of $M$. The second example fails the analogous property for arbitrary infinite density. Finally, we introduce the metric version of the concept of locally complemented Banach subspace, and prove some metric analogues to the linear theory.