switch ($hook) {
  case 'node':
  $vars['lesson_number'] = '';
    foreach($vars['node']->taxonomy as $key => $keycontent) {
      if ($keycontent->vid != 1) {
        unset($vars['taxonomy']['taxonomy_term_'. $key]);
      }
      elseif ($keycontent->vid == 3) {
        $vars['lesson_number'] = $key
      }
    }
    $vars['terms'] = theme('links', $vars['taxonomy'],  array('class' => 'links inline'));

  break;
}