span class="pre">(u,v)</span></tt> to the graph. The return type itself is
unspecified, but the type can be copy-constructed and implicitly
converted into a <tt class="docutils literal"><span class="pre">std::pair&lt;edge_descriptor,bool&gt;</span></tt>. The edge
descriptor describes the added (or found) edge. For graphs that do not
allow parallel edges, if the edge
is already in the graph then a duplicate will not be added and the
<tt class="docutils literal"><span class="pre">bool</span></tt> flag will be