;&nbsp;&nbsp;&nbsp;<span class="keyword">val</span>&nbsp;is_empty&nbsp;:&nbsp;t&nbsp;<span class="keywordsign">-&gt;</span>&nbsp;bool<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">val</span>&nbsp;mem&nbsp;:&nbsp;elt&nbsp;<span class="keywordsign">-&gt;</span>&nbsp;t&nbsp;<span class="keywordsign">-&gt;</span>&nbsp;bool<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">val</span>&nbsp;add&nbsp;:&nbsp;elt&nbsp;<span class="keywordsign">-&gt;</span>&nbsp;t&nbsp;<span class="keywords