y</span><span> = <a href="../index.html#type-id">id</a></span></code></div></div><div class="odoc-spec"><div class="spec type" id="type-t" class="anchored"><a href="#type-t" class="anchor"></a><code><span><span class="keyword">type</span> <span>!+'a t</span></span></code></div></div><div class="odoc-spec"><div class="spec value" id="val-empty" class="anchored"><a href="#val-empty" class="anchor"></a><code><span><span class="keyword">val</span> empty : <span><span class="type-var">'a</span> <a href="#type-t"