/**
  * Is node visible?
  *
  * @param mixed $a_node node object/array
  * @return boolean node visible true/false
  */
 function isNodeVisible($a_node)
 {
     include_once "./Modules/LearningModule/classes/class.ilLMTracker.php";
     return ilLMTracker::_isNodeVisible($a_node);
 }