<h2>Complexity</h2>
<p>
  All iterator operations must take amortized constant time.
  </p>
</div>
<div class="refsect1">
<a name="id-1.3.49.3.7.10"></a><h2>Invariants</h2>
<div class="variablelist"><dl class="variablelist">
<dt><span class="term">Predecrement must return object</span></dt>
<dd><p>
  <code class="computeroutput">&amp;i = &amp;(++i)</code>
  </p></dd>
<dt><span class="term">Unique path through sequence</span></dt>
<dd><p>
  <code class="computeroutput">i == j</code> implies <code class="comp