On improving efficiency of model checking through systematically ...

4.4 Subway system
This case study is a subway regulation system taken from [22]. It concerns
a (simplified version of a) speed regulation system avoiding collision. Each
train detects beacons that are placed along the track, and receives the “clock
tick” from a central clock. Ideally, a train encounters one beacon each clock
tick. The space between beacons rules the speed of the train. Now, a
train adjusts its speed as follows: let b and s be respectively the number of
encountered beacons and the number of received clock ticks.
• When b ≥ s + 10, the train notices it is early, and puts on the brake
as long as b>s. Continously braking makes the train stop before
encountering 10 beacons (using a counter c).
• When b ≤ s − 10, the train is late, and will be considered late as long
as b