.addEqualityGroup(Range.atLeast(1), Range.downTo(1, CLOSED))
        .addEqualityGroup(Range.greaterThan(1), Range.downTo(1, OPEN))
        .addEqualityGroup(Range.atMost(7), Range.upTo(7, CLOSED))
        .addEqualityGroup(Range.lessThan(7), Range.upTo(7, OPEN))
        .addEqualityGroup(Range.open(1, 7), Range.range(1, OPEN, 7, OPEN))
        .addEqualityGroup(Range.openClosed(1, 7), Range.range(1, OPEN, 7, CLOSED))

    ImmutableSortedSet<C> subSet(Range<C> range) {
      return subRangeSet(range).asSet(domain);
    }

    @Override
    ImmutableSortedSet<C> headSetImpl(C toElement, boolean inclusive) {
      return subSet(Range.upTo(toElement, BoundType.forBoolean(inclusive)));
    }

    @Override
    ImmutableSortedSet<C> subSetImpl(
        C fromElement, boolean fromInclusive, C toElement, boolean toInclusive) {

	if err = z.serverPools[poolIdx].sets[setIdx].healErasureSet(ctx, tracker.QueuedBuckets, tracker); err != nil {
		return err
	}

	// if objects have failed healing, we attempt a retry to heal the drive upto 3 times before giving up.
	if tracker.ItemsFailed > 0 && tracker.RetryAttempts < 4 {
		tracker.RetryAttempts++

	return func() error {
		// NOTE: Healing on meta is run regardless
		// of any bucket being selected, this is to ensure that
		// meta are always upto date and correct.
		return objAPI.HealObjects(h.ctx, minioMetaBucket, metaPrefix, h.settings, func(bucket, object, versionID string, scanMode madmin.HealScanMode) error {
			if h.isQuitting() {
				return errHealStopSignalled