ified vertex set.  The
    edges of the subgraph are induced by the vertex set. That is,
    every edge in the parent graph (which is <i>this</i> graph) that
    connects two vertices in the subgraph will be added to the
    subgraph.

<hr>
<pre>
vertex_descriptor local_to_global(vertex_descriptor u_local) const
</pre>
    Converts a local vertex descriptor to the corresponding global
    vertex descriptor.

<hr>
<pre>
vertex_descriptor global_to_local(vertex_descriptor u_global) const
</pre>
    Converts a