 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 have
   different lengths.<br>
</div>
<pre><span id="VALmem"><span class="keyword">val</span> mem</span> : <code class="type">'a -&gt; 'a list -&gt; bool</code></pre><div class="info">
<code class="code">mem a l</code> is true if and only if <code class="code">a</code> is