Going back in the past requires checkpointing the past, which can be very expensive, but maybe cheaper with the right kind of time-indexed data structures under

Going back in the past requires checkpointing the past, which can be very expensive, but maybe cheaper with the right kind of time-indexed data structures underlying your programs. So you just wind back time and begin fixing data structures with your backward change until you are consistent at head time again. But uhm, if you actually want the future to affect the past formally, that is going to be something really different, so I’m not really sure.