code: def is_valid_pred_string(predstr):
      
      predstr = predstr.strip('"').lstrip("'")
      # this is a stricter regex than in Pred, but doesn't check POS
      return re.match(
          r'_([^ _\\]|\\.)+_[a-z](_([^ _\\]|\\.)+)?(_rel)?$'
          r'|[^_]([^ \\]|\\.)+(_rel)?$',
          predstr
      ) is not None
docs: Return `True` if *predstr* is a valid predicate string.
  
      Examples:
          >>> is_valid_pred_string('"_dog_n_1_rel"')
          True
          >>> is_valid_pred_string('_dog_n_1')
          True
          >>> is_valid_pred_string('_dog_noun_1')
          False
          >>> is_valid_pred_string('dog_noun_1')
          True