code: static Symmetry010Date ofEpochDay(long epochDay) {
          EPOCH_DAY_RANGE.checkValidValue(epochDay + 3, ChronoField.EPOCH_DAY);
          long zeroDay = epochDay + DAYS_0001_TO_1970 + 1;
          long year = 1 + ((293 * zeroDay) / DAYS_PER_CYCLE);
          long doy = zeroDay - (DAYS_IN_YEAR * (year - 1) + Symmetry010Chronology.getLeapYearsBefore(year) * DAYS_IN_WEEK);
  
          if (doy < 1) {
              year--;
              doy += INSTANCE.isLeapYear(year) ? DAYS_IN_YEAR_LONG : DAYS_IN_YEAR;
          }
  
          int diy = INSTANCE.isLeapYear(year) ? DAYS_IN_YEAR_LONG : DAYS_IN_YEAR;
          if (doy > diy) {
              doy -= diy;
              year++;
          }
          return ofYearDay((int) year, (int) doy);
      }
docs: Obtains a {@code Symmetry010Date} representing a date in the Symmetry010 calendar
  system from the epoch-day.
  
  @param epochDay  the epoch day to convert based on 1970-01-01 (ISO), corresponds to 1970-01-04 (Sym010)
  @return the date in Symmetry010 calendar system, not null
  @throws DateTimeException if the epoch-day is out of range