code: def normalize_pred_string(predstr):
      
      tokens = [t for t in split_pred_string(predstr)[:3] if t is not None]
      if predstr.lstrip('\'"')[:1] == '_':
          tokens = [''] + tokens
      return '_'.join(tokens).lower()
docs: Normalize the predicate string *predstr* to a conventional form.
  
      This makes predicate strings more consistent by removing quotes and
      the `_rel` suffix, and by lowercasing them.
  
      Examples:
          >>> normalize_pred_string('"_dog_n_1_rel"')
          '_dog_n_1'
          >>> normalize_pred_string('_dog_n_1')
          '_dog_n_1'