INTERACTING PARTICLES
                                  by
                         Carlangelo Liverani
           
ABSTRACT:
We discuss a manifold of systems that generalize, 
in various ways, the standard 
billiards. To be able to present many of the results in a unified 
fashion we start by summarizing a general theory of the statistical 
properties of Hamiltonian systems with discontinuities. Then the 
actual examples are presented.