docs: def merge(d1, d2):
      """Merge two raw datasets into one.
  
      Parameters
      ----------
      d1 : dict
      d2 : dict
  
      Returns
      -------
      dict
      """
      if d1['formula_id2latex'] is None:
          formula_id2latex = {}
      else:
          formula_id2latex = d1['formula_id2latex'].copy()
      formula_id2latex.update(d2['formula_id2latex'])
      handwriting_datasets = d1['handwriting_datasets']
      for dataset in d2['handwriting_datasets']:
          handwriting_datasets.append(dataset)
      return {'formula_id2latex': formula_id2latex,
              'handwriting_datasets': handwriting_datasets}