  </li>
  <li>The <code class="language-c++ highlighter-rouge"><span class="n">concatenate</span></code> helper appends one list onto another.
    <ul>
      <li>If you traverse to the end of the first list, you can then attach the second list with a single pointer assignment. Neat!</li>
      <li>Joining three lists into one can be done with two calls to concatenate.</li>
      <li><code class="language-c++ highlighter-rouge"><span class="n">concatenate</span></code> must be implemented <strong>iteratively