old_contents: from .precision import Precision
  from .average_precision import AveragePrecision
  from .discounted_cumulative_gain import DiscountedCumulativeGain
  from .mean_reciprocal_rank import MeanReciprocalRank
  from .mean_average_precision import MeanAveragePrecision
  from .normalized_discounted_cumulative_gain import \
      NormalizedDiscountedCumulativeGain
  
new_contents: from .precision import Precision
  from .average_precision import AveragePrecision
  from .discounted_cumulative_gain import DiscountedCumulativeGain
  from .mean_reciprocal_rank import MeanReciprocalRank
  from .mean_average_precision import MeanAveragePrecision
  from .normalized_discounted_cumulative_gain import \
      NormalizedDiscountedCumulativeGain
  
  # TODO: unify ALIAS to list form
  
subject: Add todo.