}

    @WeakOuter
    private final class EntrySet extends ImprovedAbstractSet<Entry<R, V>> {
      @Override
      public Iterator<Entry<R, V>> iterator() {
        return new EntrySetIterator();
      }

      @Override
      public int size() {
        int size = 0;
        for (Map<C, V> map : backingMap.values()) {
          if (map.containsKey(columnKey)) {
            size++;