Rolf Klein: Geometric Firefighting.

Abstract: In 2007, A. Bressan proposed the following problem. Suppose a circular fire spreads at unit speed in the plane. What speed is needed to build, in real time, barriers that contain the fire? The problem is still open, and the difficulty seems to be with the following question. To what extent does it help to put `delaying' barriers in the fire's way that are not part of the final enclosure? We study this question in a very simple set-up and establish upper and lower bounds.