rd">val</span> is_singleton_or_more : <a href="index.html#type-t">t</a> <span>&#45;&gt;</span> <span><span>(<a href="index.html#type-key">key</a> * <a href="index.html#type-value">value</a>)</span> <a href="../../IStdlib/IContainer/index.html#type-singleton_or_more">IStdlib.IContainer.singleton_or_more</a></span></code></dt><dt class="spec value" id="val-fold_map"><a href="#val-fold_map" class="anchor"></a><code><span class="keyword">val</span> fold_map : <a href="index.html#type-t">t</a> <span>&#45;&gt;</s