module airportOpsClassroom

sig Location {
  adj: some Location
}

abstract sig Fixed {
  at: set Location
}
fact PhysicalConstraints {
  ~adj in adj
  all f: Fixed | some f.at 
  all s: State, l: Location | lone l.(~(s.loc)) & Plane //(2)
  all f: Fixed | all disj l, l': f.at |  l in l'.(^adj)

}
sig Runway, Gate, Taxiway extends Fixed {}

abstract sig Mobile {}
sig Plane, Vehicle extends Mobile {}

sig State {
  loc: Mobile -> lone Location
}