  It is shown that the electron wave vector in a crystal cannot be smaller than
a certain value. As a result, in a crystal there are many first Brillouin
zones, and not only one as it had been supposed earlier. In crystal there can
be many electrons with the same wave vector, and not only two as it had been
supposed earlier. These electrons must be at sufficiently large distances from
each other. An attempt is made to explain the decrease of electric and thermal
conductivity with decreasing crystal size.
