estimate based on evidence from both sides so well you can do it as an exercise see if you can work through that if you want to check if you really understood the derivations that we're done in the previous lecture for the common filter you could see if you can find the derivations for the backward pass the forward pass will stay the same the backward pass will be the new thing can you find what that looks like and if you can do that then means really understood how this works now we can also look at the results the imagine