#type-t">t</a></code></dt><dd><p>returns valid value when the exponant is a singleton positive integer. fails otherwise</p></dd></dl><dl><dt class="spec value" id="val-n_root"><a href="#val-n_root" class="anchor"></a><code><span class="keyword">val</span> n_root : <a href="index.html#type-t">t</a> <span>&#45;&gt;</span> <a href="index.html#type-t">t</a> <span>&#45;&gt;</span> <span><a href="index.html#type-t">t</a> option</span></code></dt><dt class="spec value" id="val-exp"><a href="#val-exp" class="anchor