t returns <code>None</code> when the given list is empty and <code>into</code> is <code>None</code>.</p></div></div><div class="odoc-spec"><div class="spec value anchored" id="val-filter_normal"><a href="#val-filter_normal" class="anchor"></a><code><span><span class="keyword">val</span> filter_normal : <span><a href="Domain/index.html#type-t">Domain.t</a> <span class="arrow">&#45;&gt;</span></span> <a href="Domain/index.html#type-t">Domain.t</a></span></code></div><div class="spec-doc"><p>Refines the abstra