private int GetDaysInFirstWeek(int year, JulianCalendarSystem calendar)
 {
     // Some of the first few days of the week year may be in the previous week year.
     // However, the whole of the first week of the week year definitely occurs
     // within the first 13 days of January.
     return Enumerable.Range(1, 13)
                      .Count(day => new LocalDate(year, 1, day, calendar).WeekOfWeekYear == 1);
 }
 static JulianCalendarSystem()
 {
     instances = new JulianCalendarSystem[7];
     for (int i = 0; i < 7; i++)
     {
         instances[i] = new JulianCalendarSystem(i + 1);
     }
 }