@Override
	public String getExtendedTwinRoomIDs(final Room R1,final Room R2)
	{
		final String R1s=getExtendedRoomID(R1);
		final String R2s=getExtendedRoomID(R2);
		if(R1s.compareTo(R2s)>0)
			return R1s+"_"+R2s;
		else
			return R2s+"_"+R1s;
	}