  First, we show that, if there are no bound states, we can express the q.m.
third cluster - involving 3 and fewer particles in Statistical Mechanics - as a
formula involving adiabatic eigenphase shifts. This is for Boltzmann
statistics.
  From this q.m. formulation, in the case of purely repulsive forces, we
recover, as h goes to 0, the classical expressions for the cluster.
  We then discuss difficulties which arise in the presence of 2-body bound
states and present a tentative formula involving eigenphase shifts and the 2
and 3 body bound state energies. We emphasize that important difficulties have
not been resolved.
