and the back traveling of the signal just I think is very is very very very slow if even possible and so it's generally not invertible or inverse compute capable so this is one reason why that prop seems unlikely and then the second reason here is error signals are signed and potentially extreme valued and i want to add to that they also just talk about this somewhere that error signals are of a different type right that's a different type so first let's see what signed error signals are signed yes we need to be