 //...
    typedef typename graph_traits&lt;Graph&gt;
      ::vertex_descriptor Vertex;

    void operator()(const Vertex&amp; v) const
    {
      //...
    }
    //...
  };
</pre>
<p>&nbsp;
<h3>Out-Edges, In-Edges, and Edge Descriptors</h3>
<p>The out-edges of a vertex are accessed with the <a href="IncidenceGraph.html#sec:out-edges"><tt>out_edges()</tt></a>
function of the <a href="IncidenceGraph.html">IncidenceGraph</a> interface. The <tt>out_edges()</tt>
function takes two arguments: the first argument