return false;
      }
    }
  }

  @LazyInit @CheckForNull private transient ColumnMap columnMap;

  @Override
  public Map<C, Map<R, V>> columnMap() {
    ColumnMap result = columnMap;
    return (result == null) ? columnMap = new ColumnMap() : result;
  }

  @WeakOuter
  private class ColumnMap extends ViewCachingAbstractMap<C, Map<R, V>> {