ote>

IN: <tt>distance_zero(D zero)</tt> 
<blockquote>
  The <tt>zero</tt> value must be the identity element for the
  <a href="./Monoid.html">Monoid</a> formed by the distance values
  and the <tt>combine</tt> function object.
  The type \code{D} is the value type of the \code{DistanceMap}
  <b>Default:</b> <tt>D()</tt>
</blockquote>

UTIL/OUT: <tt>color_map(ColorMap c_map)</tt> 
<blockquote>
  This is used during the execution of the algorithm to mark the
  vertices. The vertices start out white and beco