
it is also possible to add and remove vertices with the <a href="MutableGraph.html#sec:add-vertex"><tt>add_vertex()</tt></a>
and <a href="MutableGraph.html#sec:remove-vertex"><tt>remove_vertex()</tt></a>
functions, also of the <a href="MutableGraph.html">MutableGraph</a> interface.
<h2>Accessing the Vertex Set</h2>
<p>Now that we have created a graph, we can use the graph interface to access
the graph data in different ways. First we can access all of the vertices in the
graph using the <a href="VertexList