  The problem of two interacting particles moving in a d-dimensional billiard
is considered here. A suitable coordinate transformation leads to the problem
of a particle in an unconventional hyperbilliard. A dynamical map can be
readily constructed for this general system, which greatly simplifies
calculations. As a particular example, we consider two identical particles
interacting through a screened Coulomb potential in a one-dimensional billiard.
We find that the screening plays an important role in the dynamical behavior of
the system and only in the limit of vanishing screening length can the
particles be considered as bouncing balls. For more general screening and
energy values, the system presents strong non-integrability with resonant
islands of stability.
