boolean DateCalc_check_date(Z_int year, Z_int month, Z_int day)
{
    if ((year >= 1) and
        (month >= 1) and (month <= 12) and
        (day >= 1) and
        (day <= DateCalc_Days_in_Month_[DateCalc_leap_year(year)][month]))
            return(true);
    return(false);
}