nsensitive manner. This case-insensitivity must be implemented using a case-insensitive
 <code>Comparator</code>, such as <code>String.CASE_INSENSITIVE_ORDER</code>.</li>

 <li>The following methods must throw <code>UnsupportedOperationException</code>: <code>clear()</code>,
 <code>remove()</code>.</li>
 <li>The <code>entrySet()</code> method must return a <code>Set</code> that has the following behavior:
 <ul>
 <li>Throw <code>UnsupportedOperationException</code> for any attempt to add or remove entries fr