plore()</tt> method. In this case
we only want to be notified about edges in the shortest-paths tree so we specify
<tt>tree_edge_tag</tt>.
<p>As a finishing touch, we create a helper function to make it more convenient
to create predecessor visitors. All BGL visitors have a helper function like
this.
<p>&nbsp;
<pre>
  template &lt;class PredecessorMap&gt;
  record_predecessors&lt;PredecessorMap&gt;
  make_predecessor_recorder(PredecessorMap p) {
    return record_predecessors&lt;PredecessorMap&gt;(p);
  }
<