code: def size(self):
          
          n = self.number_of_singleton_referents()
          targets = list(self.iter_referents_tuples())
          n_targets = len(targets)
          if n == 0 or n_targets == 0:
              return  0
  
          #if len(self.__dict__['deferred_effects']) != 0:
          #    return -1 
          size1 = len(list(self.iter_referents_tuples()))
          tlow, thigh = self['targetset_arity'].get_tuple()
          clow, chigh = self['contrast_arity'].get_tuple()
          return size1
docs: Returns the size of the belief state.
  
          Initially if there are $n$ consistent members, (the result of `self.number_of_singleton_referents()`) 
          then there are generally $2^{n}-1$ valid belief states.