docs: def _get_collisions(indices):
      # type: (...) -> Dict[int, List[int]]
      """
      Return a dict ``{column_id: [possible term ids]}``
      with collision information.
      """
      collisions = defaultdict(list)  # type: Dict[int, List[int]]
      for term_id, hash_id in enumerate(indices):
          collisions[hash_id].append(term_id)
      return dict(collisions)