 efficient.</p>
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<pre><span id="VALconcat"><span class="keyword">val</span> concat</span> : <code class="type">'a list list -&gt; 'a list</code></pre><div class="info ">
<div class="info-desc">
<p>Concatenate a list of lists.  The elements of the argument are all
   concatenated together (in the same order) to give the result.
   Not tail-recursive
   (length of the argument + length of the longest sub-list).</p>
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<pre><span id="VALflatten"><span class="keyword">val</span> flatte