hes the iterator of tuples <code>TupleIterator</code> for a tuple whose
  <code>N</code>th element compares equal to <code>Key</code>. Returns <code>Tuple</code> if such a
  tuple is found, otherwise <code>false</code>.</p>
 
  The iterator will be evaluated until a match is found. If no match
  is found, infinite iterators will never return.</p>

<h3 class="function"><a name="keymap-3">keymap/3</a></h3>
<div class="spec">
<p><tt>keymap(Fun, N, TupleIterator1) -&gt; TupleIterator2</tt>
<ul class="definition