 in-edge <tt class="docutils literal"><span class="pre">e</span></tt>, <tt class="docutils literal"><span class="pre">target(e,</span> <span class="pre">g)</span> <span class="pre">==</span> <span class="pre">v</span></tt> and <tt class="docutils literal"><span class="pre">source(e,</span>
<span class="pre">g)</span> <span class="pre">==</span> <span class="pre">u</span></tt> for some vertex <tt class="docutils literal"><span class="pre">u</span></tt> that is adjacent to <tt class="docutils literal"><span c