=+when appropriate. It should call three 'phase' sub-routines which respectively determine the time of the next event, call the immediate activity routine(s) concerned, and then scan and initiate any other possible activities; and a set of task-specific activity routines which, when their condition(s) are satisfied, simulate the activities of the system being modelled and update the system state accordingly. Use a twodimensional array as an activity list which lists the next due times of the B-type activities. The 'next due' time can then be found easily by scanning this list.)