7. 1 Definitions and notations ■ Reactive system The intuition is that a transition system consists of a set of possible states for the system and a set of transitions - or state changes which the system can effect when a state change is the result of an external event or of an action made by the system, then that transition is labeled with that event or action Particular states or transitions in a transition system can be distinguished7.1 Definitions and notations ◼ Reactive System ◼ The intuition is that a transition system consists of a set of possible states for the system and a set of transitions - or state changes - which the system can effect. ◼ When a state change is the result of an external event or of an action made by the system, then that transition is labeled with that event or action. ◼ Particular states or transitions in a transition system can be distinguished