code: private static long firstMondayOfFirstWeek(int year) {
  		final long janFirst = ymdToJulian(year, 1, 1);
  		final long janFirstDow = floorMod(janFirst + 1, 7); // sun=0, sat=6
  		return janFirst + (11 - janFirstDow) % 7 - 3;
  	}
docs: Returns the first day of the first week of a year.
  Per ISO-8601 it is the Monday of the week that contains Jan 4,
  or equivalently, it is a Monday between Dec 29 and Jan 4.
  Sometimes it is in the year before the given year.