code: @Override
      public boolean isLeapYear(long prolepticYear) {
          return Math.floorMod(prolepticYear + getISOLeapYearCount(prolepticYear) + yearZeroDifference, 7) == 0
                  || Math.floorMod(prolepticYear + getISOLeapYearCount(prolepticYear + 1) + yearZeroDifference, 7) == 0;
      }
docs: Checks if the specified year is a leap year.
  <p>
  An Accounting proleptic-year is leap if the time between the end of the previous year
  and the end of the current year is 371 days.
  This method does not validate the year passed in, and only has a
  well-defined result for years in the supported range.
  
  @param prolepticYear  the proleptic-year to check, not validated for range
  @return true if the year is a leap year