For this portion of the project, you will need to write an Alloy model for use in
specifying the RoutePlanner system.
Write code for signatures and facts which will do the following:
Declare the existence of a “travel stop” type.
Declare the existence of a “route” type, which consists of an ordered
sequence of travel stops.
Declare the existence of a “time” type, representing time of day.
We will assume that routes always represent routes suggested by a planner app
(rather than simply “possible” routes).
Include an assertion that a route from starting stop A to ending stop B has exactly
the same number of items in it as the reverse trip.
Include an assertion that a route from any stop to itself consists of only one stop.
Include explanatory comments in your model code.