public Group setClasses(HashMap<Field, Time> aClasses)	{
		
		//System.out.println("Group.setClasses() : " + this + " " + aClasses);
		
		if (aClasses != null)
			this.classes = aClasses;
		
		for (Field f : this.classes.keySet())
			if (!this.done.containsKey(f))
				this.done.put(f, false);
		
		return this;
	}