  In 1985 Xiao Gang proved that the bicanonical system of a complex surface $S$
of general type with $p_2(S)>2$ is not composed of a pencil [Bull. Soc. Math.
France, 113 (1985), 23--51]. When in the end of the 80's it was finally proven
that $| 2K_S|$ is base point free, whenever $p_g\geq 1$, the part of this
theorem concerning surfaces with $p_g\geq 1$ became trivial.
  In this note a new proof of this theorem for surfaces with $p_g=0$ is
presented.
