                   traversal_category&lt;_&gt;, boost::vertex_list_graph_tag
               &gt;
           &gt;)</strong> ))

    (optional
      (visitor, *, boost::dfs_visitor&lt;&gt;()) // not checkable

      (root_vertex
        , (vertex_descriptor&lt;graphs::graph::_&gt;)
        , *vertices(graph).first)

      (index_map
        , <strong>*(boost::mpl::and_&lt;
              boost::is_integral&lt;value_type&lt;_&gt; &gt;
            , boost::is_same&lt;
                  vertex_descriptor&lt;graph