There are two ways to tell if the timing belt has been replaced. One is obvious-you are looking at a service receipt showing the replacement.
Swimlane diagrams are used whenever you need to show activities, tasks, or process steps which are being performed by different actors/roles. You can use swimlanes to group activities in an activity diagram or process flow by any category what you need: by role, by system, by department, etc.
The purpose of that fence was to keep toddlers from tumbling in, not to contain a golden that we didn't have yet. The pool is covered with a winter cover for 6 months a year. It fills up with water and it attracts ducks in the spring. I consider that Invisible Fence a lifesaver.