PowerSet(Set<E> input) {
      checkArgument(
          input.size() <= 30, "Too many elements to create power set: %s > 30", input.size());
      this.inputSet = Maps.indexMap(input);
    }

    @Override
    public int size() {
      return 1 << inputSet.size();
    }

    @Override
    public boolean isEmpty() {
      return false;
    }