code: public Boolean Add( CalendarPeriodAssociative<T> period, AddFunction<T> addFunction )
  	{
  		// combine les deux tableaux dans ordre croissant
  		List<PeriodAssociative<T>> combined = _Combine( periods, period.getPeriods() );
  
  		// merge overlapping periods
  		List<PeriodAssociative<T>> result = _Merge( combined, addFunction );
  		if( result == null )
  			return null; // we should stop the MakeUpCalendarAssociative process
  
  		periods = result;
  
  		// to say we can continue...
  		return true;
  	}
docs: adding two associative periods