&gt; 'a list -&gt; 'b list -&gt; init:'c -&gt; 'c</code></pre><div class="info ">
<div class="info-desc">
<p><code class="code"><span class="constructor">List</span>.fold_right2&nbsp;f&nbsp;[a1;&nbsp;...;&nbsp;an]&nbsp;[b1;&nbsp;...;&nbsp;bn]&nbsp;c</code> is
   <code class="code">f&nbsp;a1&nbsp;b1&nbsp;(f&nbsp;a2&nbsp;b2&nbsp;(...&nbsp;(f&nbsp;an&nbsp;bn&nbsp;c)&nbsp;...))</code>.
   Raise <code class="code"><span class="constructor">Invalid_argument</span></code> if the two lists are determined
   to have