/**
  * Main Sensei_Course_Progress Instance
  *
  * Ensures only one instance of Sensei_Course_Progress is loaded or can be loaded.
  *
  * @since 1.0.0
  * @static
  * @see Sensei_Course_Progress()
  * @return Main Sensei_Course_Progress instance
  */
 public static function instance($file, $version = '1.0.0')
 {
     if (is_null(self::$_instance)) {
         self::$_instance = new self($file, $version);
     }
     return self::$_instance;
 }
 /**
  * Returns the main instance of Sensei_Course_Progress to prevent the need to use globals.
  *
  * @since  1.0.0
  * @return object Sensei_Course_Progress
  */
 function Sensei_Course_Progress()
 {
     return Sensei_Course_Progress::instance(__FILE__, '1.0.6');
 }