an class="keyword">template</span><span class="special">&lt;</span><span class="keyword">typename</span> Axis<span class="special">,</span> <span class="keyword">typename</span> U<span class="special">&gt;</span> 
          <span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special">&lt;</span> <span class="keyword">int</span><span class="special">,</span> <span class="keyword">int</span> <span class="special">&gt;</span> <a class="link" href="