// Views

  /**
   * Abstract set whose {@code isEmpty()} returns whether the table is empty and whose {@code
   * clear()} clears all table mappings.
   */
  @WeakOuter
  private abstract class TableSet<T> extends ImprovedAbstractSet<T> {
    @Override
    public boolean isEmpty() {
      return backingMap.isEmpty();
    }

    @Override
    public void clear() {
      backingMap.clear();
    }