def is_valid_ymd(year, month, day):
return <NUM_LIT:1> <= month <= <NUM_LIT:12> and <NUM_LIT:1> <= day <= days_in_month(year, month) and year >= <NUM_LIT><EOL>
return True if (year,month, day) can be represented in Excel-notation
(number of days since 30.12.1899) for calendar days, otherwise False

:param int year: calendar year
:param int month: calendar month
:param int day: calendar day
:return bool: