  A quasi-particle theory for monatomic gases in equilibrium is formulated and
evaluated to yield the exact virial contributions to the thermodynamic state
functions in lowest order of the density. Van der Waals blocking has
necessarily to be accounted for in occupation number statistics. The
quasi-particle distribution function differs from the Wigner function by a
bilinear functional thereof. The progress made so far is promising with respect
to a corresponding version of kinetic theory.
