</pre><div class="info ">
<div class="info-desc">
<p>Same as <a href="List.html#VALexists"><code class="code"><span class="constructor">List</span>.exists</code></a>, but for a two-argument predicate.
   Raise <code class="code"><span class="constructor">Invalid_argument</span></code> if the two lists are determined
   to have different lengths.</p>
</div>
</div>

<pre><span id="VALmem"><span class="keyword">val</span> mem</span> : <code class="type">'a -&gt; set:'a list -&gt; bool</code></pre><div class="i