     </ul>
            </li>
            <li class="nav-item" data-level="3"><a href="#example-4-a-simple-monophonic-echo" class="nav-link">Example 4: A simple monophonic echo</a>
              <ul class="nav flex-column">
              </ul>
            </li>
            <li class="nav-item" data-level="3"><a href="#example-5-a-stereophonic-echo" class="nav-link">Example 5: A stereophonic echo</a>
              <ul class="nav flex-column">
              </ul>
            </li>
            <li class="nav-it