pre">u</span></tt> in graph <tt class="docutils literal"><span class="pre">g</span></tt>. If the graph is undirected, this iterator-range
provides access to all edges incident on vertex <tt class="docutils literal"><span class="pre">u</span></tt>. For both
directed and undirected graphs, for an out-edge <tt class="docutils literal"><span class="pre">e</span></tt>, <tt class="docutils literal"><span class="pre">source(e,</span> <span class="pre">g)</span>
<span class="pre">==</span> <span class="pre">u</span