State Transition Specifications:ASLAN Clock

SPECIFICATION Clock

LEVEL Top_Level

TYPE BellStatus IS (quiet, ringing), AlarmStatus IS (disabled, enabled)

VARIABLE time, alarm_time: INTEGER, bell: BellStatus, alarm: AlarmStatus

INITIAL (time = midnight) & (bell = quiet) & (alarm = disabled)

INVARIANT TRUE

TRANSITION tick ENTRY TRUE

EXIT (time = succ(time???? ????????  & (if ((alarm_time = time) & (alarm = enabled))  then (bell = ringing) else (bell = bell?) fi)  & (alarm = alarm?) & (alarm_time = alarm_time?)

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