On geodesic extendibility and the space of compact balls of length spaces.

In this work we study the issue of geodesic extendibility on complete and locally compact metric length spaces. We focus on the geometric structure of the space $(\Sigma (X),d_H)$ of compact balls endowed with the Hausdorff distance and give an explicit isometry between $(\Sigma (X),d_H)$ and the closed half-space $ X\times \mathbb{R}_{\ge 0}$ endowed with a taxicab metric. Among the applications we establish a group isometry between $\mbox{Iso} (X,d)$ and $\mbox{Iso} (\Sigma (X),d_H)$ when $(X,d)$ is a Hadamard space.