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<code class="code"><span class="keyword">sig</span>
&nbsp;&nbsp;<span class="keyword">type</span>&nbsp;spec&nbsp;=
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="constructor">Unit</span>&nbsp;<span class="keyword">of</span>&nbsp;(unit&nbsp;<span class="keywordsign">-&gt;</span>&nbsp;unit)
&nbsp;&nbsp;&nbsp;&nbsp;<span class="keywordsign">|</span>&nbsp;<span class="constructor">Bool</span>&nbs