docs: def non_fluents_scope(self) -> Dict[str, TensorFluent]:
          '''Returns a partial scope with non-fluents.
  
          Returns:
              A mapping from non-fluent names to :obj:`rddl2tf.fluent.TensorFluent`.
          '''
          if self.__dict__.get('non_fluents') is None:
              self._initialize_non_fluents()
          return dict(self.non_fluents)