Ideal closures of Busemann space and singular Minkowski space

Abstract

We discuss two different in general natural approaches to the ideal closure and ideal boundary of Busemann nonpositively curved metric space. It is shown that the identity map of the space admits surjective continuation from its coarse ideal closure to the weak one. We consider some situations when these closures coincide, and when they are essentially different. In particular, the singular Minkowski space is studied as flat Busemann space, and some types of its ideal points are described.