incorporate the dynamics model and the next observation and repeat then backward pass does something very similar but works its way from the back you initialize with just uniform because you have nothing really to go out there's no prior at the end you have just nothing to start from and then you start bringing in evidencing is bringing the dynamics that got you there so the dynamics into the time step you were working from but otherwise it looks exactly the same and once you have those you can combine them to get the distribution for the