tifier">a2</span> <span class="special">-</span> <span class="identifier">b2</span><span class="special">));</span>
      <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">make_tuple</span><span class="special">(</span><span class="identifier">fx</span><span class="special">,</span> <span class="identifier">dfx</span><span class="special">,</span> <span class="identifier">dfx2</span><span class="special">);</span>
   <span class="s