 global vertex descriptor to the corresponding local
    vertex descriptor.

<hr>
<pre>
edge_descriptor local_to_global(edge_descriptor e_local) const
</pre>
    Converts a local edge descriptor to the corresponding global edge
    descriptor.

<hr>
<pre>
edge_descriptor global_to_local(edge_descriptor u_global) const
</pre>
    Converts a global edge descriptor to the corresponding local edge
    descriptor.

<hr>
<pre>
std::pair&lt;vertex_descriptor, bool&gt; find_vertex(vertex_descriptor u_global) const
