  Since the Gibbs distribution function always yields a density of particles
constant in space, in order to obtain the periodic density characteristic of a
crystal it is usual to mention the method of quasi-averages. In the present
paper it is shown that the method of quasi-averages does not lead to the
periodic density as well as the initial Gibbs distribution. It is also
discussed how the crystalline state can be investigated by means of statistical
mechanics.
