@Nullable BitString intersect(BitString other) {
      long intersectMask = myMask & other.myMask;
      if ((myBits & intersectMask) != (other.myBits & intersectMask)) return null;
      return new BitString(myBits | other.myBits, myMask | other.myMask);
    }
@Nullable BitString intersect(BitString other)