@Override
          protected @Nullable Set<E> computeNext() {
            if (bits.isEmpty()) {
              bits.set(0, size);
            } else {
              int firstSetBit = bits.nextSetBit(0);
              int bitToFlip = bits.nextClearBit(firstSetBit);

              if (bitToFlip == index.size()) {
                return endOfData();
              }

              /*