y about this requirement by replacing the <tt class="docutils literal">*</tt> element
of the signature with the required type, in parentheses:</p>
<pre class="literal-block">
(root_vertex,
     <strong>(typename boost::graph_traits&lt;graph_type&gt;::vertex_descriptor)</strong>,
     *vertices(graph).first)
</pre>
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<p>Now the original <tt class="docutils literal">depth_first_search</tt> will only be called when
the <tt class="docutils literal">root_vertex</tt> argument can be converted to 