The Department of Mathematics at BZU hosted Thierry Monteil from CNRS  at the  Universite de Montepellier to talk about "Finite blocking property on polygonal billiards and translation surfaces," on 5 November 2009.  Here below is an abstract of his lecture:

A planar polygonal billiard P is said to have the finite blocking property if for every pair (O,A) of points in P there exists a finite number of "blocking" points B1,...,Bn such that every trajectory from O to A meets one of the Bi's.

This property was introduced in a problem of the the Leningrad's Olympiad in 1989, and solved there for the squared billiard table (we will see that the square has the finite blocking property). But it is not solved in the general case. The talk will focus on this property, that can be considered as a property about illumination in P. We will first introduce the basic notion of a translation surface that allow to study rational polygonal billiards.