Integer keyIndex = keyToIndex().get(key);
      return (keyIndex == null) ? null : getValue(keyIndex);
    }

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

        @Override
        @CheckForNull
        protected Entry<K, V> computeNext() {

      }

      @Override
      public boolean retainAll(Collection<?> c) {
        return removeFromColumnIf(not(in(c)));
      }
    }

    private class EntrySetIterator extends AbstractIterator<Entry<R, V>> {
      final Iterator<Entry<R, Map<C, V>>> iterator = backingMap.entrySet().iterator();

      @Override
      @CheckForNull
      protected Entry<R, V> computeNext() {

    }

    @Override
    public String toString() {
      return "orderedPermutationCollection(" + inputList + ")";
    }
  }

  private static final class OrderedPermutationIterator<E> extends AbstractIterator<List<E>> {
    @CheckForNull List<E> nextPermutation;
    final Comparator<? super E> comparator;

    OrderedPermutationIterator(List<E> list, Comparator<? super E> comparator) {

    }

    @Override
    public String toString() {
      return "orderedPermutationCollection(" + inputList + ")";
    }
  }

  private static final class OrderedPermutationIterator<E> extends AbstractIterator<List<E>> {
    @CheckForNull List<E> nextPermutation;
    final Comparator<? super E> comparator;

    OrderedPermutationIterator(List<E> list, Comparator<? super E> comparator) {

    PostOrderNode(T root, Iterator<T> childIterator) {
      this.root = checkNotNull(root);
      this.childIterator = checkNotNull(childIterator);
    }
  }

  private final class PostOrderIterator extends AbstractIterator<T> {
    private final ArrayDeque<PostOrderNode<T>> stack;

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

    @Override

      @Override
      public boolean isEmpty() {
        return set1.isEmpty() && set2.isEmpty();
      }

      @Override
      public UnmodifiableIterator<E> iterator() {
        return new AbstractIterator<E>() {
          final Iterator<? extends E> itr1 = set1.iterator();
          final Iterator<? extends E> itr2 = set2.iterator();

          @Override
          @CheckForNull

      Integer keyIndex = keyToIndex().get(key);
      return (keyIndex == null) ? null : getValue(keyIndex);
    }

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

        @Override
        @CheckForNull
        protected Entry<K, V> computeNext() {

        }
        result = size = Ints.saturatedCast(total);
      }
      return result.intValue();
    }

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

        @Override
        @CheckForNull
        protected C computeNext() {

        }
        result = size = Ints.saturatedCast(total);
      }
      return result.intValue();
    }

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

        @Override
        @CheckForNull
        protected C computeNext() {

        Iterators.mergeSorted(
            Iterables.transform(
                backingMap.values(), (Map<C, V> input) -> input.keySet().iterator()),
            comparator);

    return new AbstractIterator<C>() {
      @CheckForNull C lastValue;

      @Override
      @CheckForNull
      protected C computeNext() {
        while (merged.hasNext()) {
          C next = merged.next();