<?php

            if(ISSET ($_SESSION['user'])) { ?>

           <li><a href="logout.php">Uitloggen</a></li>

          <?php } else { ?>
          <li><a href="login.php">Aanmelden</a></li>
          <li><a href="register.php">Registeren <span class="sr-only">(current)</span></a></li>
          <?php } ?>
        </ul>
      </div><!--/.nav-collapse -->
    </div><!--/.container-fluid -->
  </nav>