}

    @Override
    public SortedMap<K, V> headMap(K toKey) {
      return standardHeadMap(toKey);
    }

    @Override
    public K lastKey() {
      return standardLastKey();
    }

    @Override
    public SortedMap<K, V> tailMap(K fromKey) {
      return standardTailMap(fromKey);
    }
  }

    }

    @Override
    public SortedMap<K, V> headMap(K toKey) {
      return standardHeadMap(toKey);
    }

    @Override
    public K lastKey() {
      return standardLastKey();
    }

    @Override
    public SortedMap<K, V> tailMap(K fromKey) {
      return standardTailMap(fromKey);
    }
  }

  /**
   * A sensible definition of {@link #lastKey} in terms of {@code lastEntry}. If you override {@code
   * lastEntry}, you may wish to override {@code lastKey} to forward to this implementation.
   */
  protected K standardLastKey() {
    Entry<K, V> entry = lastEntry();
    if (entry == null) {
      throw new NoSuchElementException();
    } else {
      return entry.getKey();
    }
  }

  @Override

  /**
   * A sensible definition of {@link #lastKey} in terms of {@code lastEntry}. If you override {@code
   * lastEntry}, you may wish to override {@code lastKey} to forward to this implementation.
   */
  protected K standardLastKey() {
    Entry<K, V> entry = lastEntry();
    if (entry == null) {
      throw new NoSuchElementException();
    } else {
      return entry.getKey();
    }
  }

  @Override