</code>.</p><p>This is equivalent to <code>List.fold_right op (NonEmptyList.tl xs)
      (NonEmptyList.hd xs)</code>.</p></dd></dl></details></div></div></div><dl><dt class="spec value" id="val-unit"><a href="#val-unit" class="anchor"></a><code><span class="keyword">val</span> unit : <a href="index.html#type-t">t</a></code></dt><dd><p><code>unit</code> is the identity element in the monoid over <a href="index.html#type-t"><code>t</code></a>.</p><p>Every implementation must ensure that for any <code>x : t</c