              A model of <a class="link" href="../../../sequence/concepts/forward_sequence.html" title="Forward Sequence">Forward
                      Sequence</a>, <code class="computeroutput"><span class="identifier">f</span><span class="special">(</span><span class="identifier">e</span><span class="special">)</span></code> must be a valid expression
                      for each element <code class="computeroutput"><span class="identifier">e</span></code>
                      in <code class="computero