urrent&nbsp;:&nbsp;unit&nbsp;<span class="keywordsign">-&gt;</span>&nbsp;t&nbsp;option<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">val</span>&nbsp;system&nbsp;:&nbsp;unit&nbsp;<span class="keywordsign">-&gt;</span>&nbsp;t&nbsp;option<br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">val</span>&nbsp;compare&nbsp;:&nbsp;t&nbsp;<span class="keywordsign">-&gt;</span>&nbsp;<span class="constructor">OpamFormula</span>.relop&nbsp;<span class="keywordsign">-&gt;</span>&nbsp;t&nbsp;<spa