text: """
  Transition namedtuple.
  """
  
  from collections import namedtuple
  
  Transition = namedtuple('Transition', ('state', 'action', 'next_state', 'reward'))
  
  TransitionTD = namedtuple('Transition', ('state', 'action', 'next_state', 'reward', 'n_next_state', 'R_cum', 'gamma_n'))