criptor u_local, vertex_descriptor v_local, subgraph&amp; g)
</pre>
    Adds edge <i>(u,v)</i> to the subgraph <i>g</i> and to all of the subgraph's
    ancestors in the subgraph tree. This function returns the edge
    descriptor for the new edge. If the edge is already in the graph
    then a duplicate will not be added and the Boolean flag will be
    false.
    (Required by <a href="EdgeMutableGraph.html">EdgeMutableGraph</a>.)

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<pre>
std::pair&lt;edge_descriptor, bool&gt;
add_edge(vertex_descripto