Those are the notes of the two talks I gave in april 2013 in St-John (US
Virgin Islands) during the Simons Symposium on non-Archimedean and tropical
geometry. They essentially consist of a survey of Hrushovski and Loeser's work
on the homotopy type of Berkovich spaces; the last section explains how the
author has used their work for studying pre-image of skeleta.Comment: 31 pages. This text will appear in the Proceedings Book of the Simons
Symposium on non-Archimedean and tropical geometry (april 2013, US Virgin
Islands). I've taken into account the remarks and suggestion of the referee