; </span><span class=identifier>x</span><span class=special>)</span><span class=keyword>const
  </span><span class=special>{
    </span><span class=keyword>return </span><span class=identifier>id</span><span class=special>&lt;</span><span class=identifier>x</span><span class=special>.</span><span class=identifier>id</span><span class=special>;
  </span><span class=special>}

  </span><span class=keyword>bool </span><span class=keyword>operator</span><span class=special>!=(</span><span class=keyword>const </