em" data-level="3"><a href="#example-2-a-sine-wave-with-volume-control" class="nav-link">Example 2: a sine wave with volume control</a>
              <ul class="nav flex-column">
              </ul>
            </li>
            <li class="nav-item" data-level="3"><a href="#example-3-exercise-add-a-frequency-control" class="nav-link">Example 3: Exercise, add a frequency control</a>
              <ul class="nav flex-column">
              </ul>
            </li>
            <li class="nav-item" data-level="3