/span><span class="n">Executor</span><span class="w"> </span><span class="n">executor</span><span class="p">;</span>

<span class="w">  </span><span class="k">const</span><span class="w"> </span><span class="kt">size_t</span><span class="w"> </span><span class="n">num_lines</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">2</span><span class="p">;</span>
<span class="w">  </span>
<span class="w">  </span><span class="c1">// a topological order of the graph</span