algebraic structure or category-theoretically as the single object in the category, with each element being a morphism <code>t -&gt; t</code>.</p></dd></dl><dl><dt class="spec value" id="val-op"><a href="#val-op" class="anchor"></a><code><span class="keyword">val</span> op : <a href="index.html#type-t">t</a> <span>&#45;&gt;</span> <a href="index.html#type-t">t</a> <span>&#45;&gt;</span> <a href="index.html#type-t">t</a></code></dt><dd><p><code>op x y</code> is an associative operation over all elements <cod