// TODO(lowasser): consider making the entries live views
        return new AbstractIterator<Entry<E>>() {
          @Override
          protected @Nullable Entry<E> computeNext() {
            if (iterator1.hasNext()) {
              Entry<? extends E> entry1 = iterator1.next();
              E element = entry1.getElement();

                  .values()
                  .iterator();
          return new AbstractIterator<Entry<Range<K>, V>>() {

            @Override
            protected @Nullable Entry<Range<K>, V> computeNext() {
              if (backingItr.hasNext()) {
                RangeMapEntry<K, V> entry = backingItr.next();
                if (entry.getUpperBound().compareTo(subRange.lowerBound) <= 0) {

      return new AbstractIterator<Entry<K, V>>() {
        private int index = -1;
        private final int maxIndex = keyToIndex().size();

        @Override
        protected @Nullable Entry<K, V> computeNext() {
          for (index++; index < maxIndex; index++) {
            V value = getValue(index);
            if (value != null) {
              return immutableEntry(getKey(index), value);
            }
          }

      this.nextPermutation = new ArrayList<>(list);
      this.comparator = comparator;
    }

    @Override
    protected @Nullable List<E> computeNext() {
      if (nextPermutation == null) {
        return endOfData();
      }
      ImmutableList<E> next = ImmutableList.copyOf(nextPermutation);
      calculateNextPermutation();
      return next;
    }

      return new AbstractIterator<Entry<K, V>>() {
        private int index = -1;
        private final int maxIndex = keyToIndex().size();

        @Override
        protected @Nullable Entry<K, V> computeNext() {
          for (index++; index < maxIndex; index++) {
            V value = getValue(index);
            if (value != null) {
              return immutableEntry(getKey(index), value);
            }
          }

      return new AbstractIterator<C>() {
        final Iterator<Range<C>> rangeItr = ranges.iterator();
        Iterator<C> elemItr = emptyIterator();

        @Override
        protected @Nullable C computeNext() {
          while (!elemItr.hasNext()) {
            if (rangeItr.hasNext()) {
              elemItr = ContiguousSet.create(rangeItr.next(), domain).iterator();
            } else {
              return endOfData();

            final Iterator<Entry<K, Collection<V>>> backingIterator =
                unfiltered.asMap().entrySet().iterator();

            @Override
            protected @Nullable Entry<K, Collection<V>> computeNext() {
              while (backingIterator.hasNext()) {
                Entry<K, Collection<V>> entry = backingIterator.next();
                K key = entry.getKey();
                Collection<V> collection =

    PostOrderIterator(T root) {
      this.stack = new ArrayDeque<>();
      stack.addLast(expand(root));
    }

    @Override
    protected @Nullable T computeNext() {
      while (!stack.isEmpty()) {
        PostOrderNode<T> top = stack.getLast();
        if (top.childIterator.hasNext()) {
          T child = top.childIterator.next();
          stack.addLast(expand(child));

      return new AbstractIterator<C>() {
        final Iterator<Range<C>> rangeItr = ranges.iterator();
        Iterator<C> elemItr = emptyIterator();

        @Override
        protected @Nullable C computeNext() {
          while (!elemItr.hasNext()) {
            if (rangeItr.hasNext()) {
              elemItr = ContiguousSet.create(rangeItr.next(), domain).iterator();
            } else {
              return endOfData();

          final Iterator<? extends E> itr1 = set1.iterator();
          final Iterator<? extends E> itr2 = set2.iterator();

          @Override
          protected @Nullable E computeNext() {
            if (itr1.hasNext()) {
              return itr1.next();
            }
            while (itr2.hasNext()) {
              E e = itr2.next();
              if (!set1.contains(e)) {