entry from the outside world or there's a driver who was busy who became available and and came back into the system who chose not to exit okay so there's some queue that's going up and down available drivers coming in and then when rides are requested this cue gets served down okay so a major sort of simplification for us and one of the reasons for exactly the lining of the assumptions we had is that this type of queueing model turns out to be what's called a Jackson Network and this is more generally true for the