  The electron-electron scattering increases the resistance of ballistic
many-mode channels whose width is smaller than their length. We show that this
increase saturates in the limit of infinitely long channels. Because the
mechanisms of angular relaxation of electrons in three and two dimensions are
different, the saturation value of the correction to the resistance is
temperature-independent in the case of three-dimensional channels and is
proportional to the temperature for two-dimensional ones. The spatial behavior
of electron distribution in the latter case is described by an unusual
characteristic length.
