  The possible ways to describe the states of a system of many hard spheres are
considered, in particular by means of functions describing correlations of
states. It is stated an approach to the description of the evolution based on
the dynamics of correlations in a system of hard spheres. In addition, we
consider another approach to describing the evolution of correlations in a
system of many hard spheres, namely, in the framework of a one-particle
distribution function (correlation function) governed by the non-Markovian
Enskog kinetic equation.
