Examples of such problems include, for example, mechanical impact problems, electrical circuits with " ideal " diodes, Coulomb friction problems for contacting bodies, and dynamic economic and related problems such as dynamic traffic networks and networks of queues ( where the constraints can either be upper limits on queue length or that the queue length cannot become negative ).
32.
This was further extended by Erol Gelenbe and Jean-Michel Fourneau with customer types called " resets " which can model the repair of failures : when a queue hits the empty state, representing ( for instance ) a failure, the queue length can jump back or be " reset " to its steady-state distribution by an arriving reset customer, representing a repair.
33.
If they get to the front before the parent is done shipping, they let one, and only one, customer past them, until that customer is checked out, then they let the next customer past them, etc . Let's assume that the shopping time is sufficiently long compared with the queue length so that the kid is always at the front by the time the parent finishes shopping.
