 valid vertex descriptor of <TT>g</TT>.<br>
Postcondition: <tt>u</tt> does not appear as a source or target of
any edge in <TT>g</TT>.
</TD>
</TR>

<tr>
<TD><a name="sec:remove-vertex"><TT>remove_vertex(u,&nbsp;g)</TT></a></TD>
<TD>
Remove <i>u</i> from the vertex set of the graph. Note that undefined
behavior may result if there are edges remaining in the graph who's
target is <i>u</i>. Typically the <TT>clear_vertex()</TT> function
should be called first.<br>
Return type: <TT>void</TT><br>
Precondition: <