" href="../../../sequence/concepts/forward_sequence.html" title="Forward Sequence">Forward
                      Sequence</a>, <code class="computeroutput"><span class="identifier">e2</span>
                      <span class="special">=</span> <span class="identifier">e1</span></code>
                      is valid expression for each pair of elements <code class="computeroutput"><span class="identifier">e1</span></code> of <code class="computeroutput"><span class="identifier">src</span></code>
            