In the normal forward process, is there a choice point at each step? How is the choice made? In a Markov process, the choices are weighted by probabilities such P(A)= x and P(B)= 1-x (if there are only two choices and 1>x>0). A Markov process is probabilistic. If you reverse it, it might be deterministic if the nature of the program is for the return path to follow the outward path back to its original initial state. On the other hand, if the outward path is fully determined, I don't see how the return path can be probabilistic unless programed to be so. This can't be done simply by reversing the original program afaik.