TT>u</TT> is a valid vertex descriptor of <TT>g</TT>.<br>
Postcondition: <TT>num_vertices(g)</TT> is one less, <TT>u</TT>
no longer appears in the vertex set of the graph and it
is no longer a valid vertex descriptor.
</TD>
</TR>
</TABLE>

<P>
</LI>
</UL>

<P>

<H3>Complexity Guarantees</H3>

<P>

<UL>
<LI>Edge insertion must be either amortized constant time or it
 can be <i>O(log(E/V))</i> if the insertion also checks to
  prevent the addition of parallel edges (which is a ``feature'' of
  some graph type