• Represent operators and their actions.
  

[Mr_Squire, notify(HQ)]incorrect_fire_notification
- The result of Mr Squire notifying HQ would be that
- the position of the fire is incorrectly recorded



[PC_bebbington, Leaves_Underground]
      [PC_bebbington, Calls(HQ)]HQ_Informed
- The result of PC Bebbington notifying HQ would be that
- the position of the fire is correctly recorded

• Can reason about:
  - effects of same action by different users.