}

    @Override
    public String toString() {
      return "BY_TO_STRING";
    }

    private Object readResolve() {
      return INSTANCE;
    }
  }

  // Always equal is a valid total ordering. And it works for any Object.
  private static final class AlwaysEqual extends Ordering<@Nullable Object>
      implements Serializable {
    private static final AlwaysEqual INSTANCE = new AlwaysEqual();

    }

    @Override
    public String toString() {
      return "BY_TO_STRING";
    }

    private Object readResolve() {
      return INSTANCE;
    }
  }

  // Always equal is a valid total ordering. And it works for any Object.
  private static final class AlwaysEqual extends Ordering<@Nullable Object>
      implements Serializable {
    private static final AlwaysEqual INSTANCE = new AlwaysEqual();