lass="special">);</span>

  <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">make_pair</span><span class="special">(</span>
    <span class="special">(</span><span class="identifier">minus_b</span> <span class="special">-</span> <span class="identifier">sqrt</span><span class="special">(</span><span class="identifier">minus_b</span> <span class="special">*</span> <span class="identifier">minus_b</span> <span class="special">-</spa