---<code>0</code>
in this case---and the first element of <code>numbers</code>, returning the sum:
<code>1</code>.</li>
<li>The closure is called again repeatedly with the previous call's return
value and each element of the sequence.</li>
<li>When the sequence is exhausted, the last value returned from the
closure is returned to the caller.</li>
</ol>
<p>If the sequence has no elements, <code>nextPartialResult</code> is never executed
and <code>initialResult</code> is the result of the call to <code>reduce