code: public Tune removeTune(int referenceNumber) {
  		Tune ret = super.removeTune(referenceNumber);
  		if (ret != null) {
  			notifyListenersForTuneChange(new TuneChangeEvent(this,
  					TuneChangeEvent.TUNE_REMOVED, ret));
  		}
  		return ret;
  	}
docs: Removes the tune having the requested reference number from the book
  
  @param referenceNumber
  @return the removed tune, null if didn't exist.