e-var">'a</span></code></dt><dd><p>misc</p></dd></dl><dl><dt class="spec value" id="val-fold_on_combination_2"><a href="#val-fold_on_combination_2" class="anchor"></a><code><span class="keyword">val</span> fold_on_combination_2 : <span>?&#8288;duplicate:bool</span> <span>&#45;&gt;</span> <span>(<span class="type-var">'a</span> <span>&#45;&gt;</span> <span class="type-var">'b</span> <span>&#45;&gt;</span> <span class="type-var">'b</span> <span>&#45;&gt;</span> <span class="type-var">'a</span>)</span> <span>&