an class="special">::</span><span class="identifier">pair</span></code>
        in some circumstances, but that class is cumbersome to use because we need
        to specify two template arguments, and for all range algorithm purposes we
        must enforce the two template arguments to be the same. Moreover, <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special">&lt;</span><span class="identifier">iterator</s