Use the right tag to close this unordered list.

<html>
<body>
  Mathematical Constants
  <ul>
   <li>Archimedes' Constant (Pi)</li>
   <li>Euler's Number (e)</li>
   <li>The Golden Ratio</li>
  </ul>
</body>
</html>]]>

To close the unordered list, add the </ul> tag.