tional Traversal Concept">Bidirectional
        Traversal Concept</a>
</h4></div></div></div>
<p>
          A class or built-in type <code class="computeroutput"><span class="identifier">X</span></code>
          models the <span class="bold"><strong>Bidirectional Traversal</strong></span> concept
          if, in addition to <code class="computeroutput"><span class="identifier">X</span></code> meeting
          the requirements of Forward Traversal Iterator, the following expressions
          are valid an