public Flag CheckError()
    {
      boolean error = (lift.f == Flag.AMBER || lift.f == Flag.RED || drag.f == Flag.AMBER || drag.f == Flag.RED);
      
      if(error)
      {
          blacklist.add(param);
      }
      
      Flag f = Flag.GREEN;
                 
                 if(lift.f == Flag.AMBER || drag.f == Flag.AMBER)
                 {
                     f = Flag.AMBER;
                 }
                 
                 if(lift.f == Flag.RED || drag.f == Flag.RED)
                 {
                     f = Flag.RED;
                 }
      
      return f;
    }