-- Opal test
IMPLEMENTATION LeapYear
IMPORT Nat COMPLETELY
DEF leapYear(year) ==
IF (year % ("400"!) = 0) THEN true
IF (year % ("400"!) |= 0) and (year % 100 = 0) THEN false
IF (year % 100 |= 0) and (year % 4 = 0) THEN true
IF (year % 4 |= 0) THEN false
FI