ImmutableSetMultimap.Builder<String, Integer> builder = new Builder<>();
    StringHolder holder = new StringHolder();
    holder.string = "one";
    Entry<String, Integer> entry =
        new AbstractMapEntry<String, Integer>() {
          @Override
          public String getKey() {
            return holder.string;
          }

          @Override
          public Integer getValue() {

    }
    return new Itr<Entry<K, V>>() {
      @Override
      Entry<K, V> getOutput(int entry) {
        return new MapEntry(entry);
      }
    };
  }

  final class MapEntry extends AbstractMapEntry<K, V> {
    @ParametricNullness private final K key;

    private int lastKnownIndex;

    MapEntry(int index) {
      this.key = key(index);
      this.lastKnownIndex = index;
    }

        while (iterator.hasNext()) {
          Entry<R, Map<C, V>> entry = iterator.next();
          if (entry.getValue().containsKey(columnKey)) {
            @WeakOuter
            final class EntryImpl extends AbstractMapEntry<R, V> {
              @Override
              public R getKey() {
                return entry.getKey();
              }

              @Override
              public V getValue() {

    }
    return new Itr<Entry<K, V>>() {
      @Override
      Entry<K, V> getOutput(int entry) {
        return new MapEntry(entry);
      }
    };
  }

  final class MapEntry extends AbstractMapEntry<K, V> {
    @ParametricNullness private final K key;

    private int lastKnownIndex;

    MapEntry(int index) {
      this.key = key(index);
      this.lastKnownIndex = index;
    }

          return backingIterator.hasNext();
        }

        @Override
        public Entry<K, ImmutableSet<V>> next() {
          Entry<K, V> backingEntry = backingIterator.next();
          return new AbstractMapEntry<K, ImmutableSet<V>>() {
            @Override
            public K getKey() {
              return backingEntry.getKey();
            }

            @Override

          return backingIterator.hasNext();
        }

        @Override
        public Entry<K, ImmutableSet<V>> next() {
          Entry<K, V> backingEntry = backingIterator.next();
          return new AbstractMapEntry<K, ImmutableSet<V>>() {
            @Override
            public K getKey() {
              return backingEntry.getKey();
            }

            @Override