@Override
	public boolean eraseValue(LabItem lab) 
	{
		if(lab == null)
		{
			return false;
		}
		Iterator<LectureItem> it = workingItems.keySet().iterator();
		LectureItem current;
		while (it.hasNext()) 
		{
			current = it.next();

			if(matchs(current, lab))
			{
				workingItems.put(current, null);
				return true;
			}
		}
		return false;
	}