Axiomatic Specifications:VDM Clock
ext wr time: N, bell: {quiet, ringing}, alarm: {disabled, enabled}
post (time? = midnight) ???(bell? = quiet) ? (alarm?= disabled)
ext wr time: N, bell: {quiet, ringing}
rd alarm_time: N, alarm: {disabled, enabled}
post (time? = succ(time)) ? (if (alarm_time? = time?) ? (alarm? = enabled) then (bell? = ringing) else (bell? = bell)