code: def sample_forward_transitions(self, batch_size, batch_info, forward_steps: int,
                                     discount_factor: float) -> Transitions:
          
          raise NotImplementedError
docs: Sample transitions from replay buffer with _forward steps_.
          That is, instead of getting a transition s_t -> s_t+1 with reward r,
          get a transition s_t -> s_t+n with sum of intermediate rewards.
  
          Used in a variant of Deep Q-Learning