at the actual time to also incorporate it to get the full evidence alright so in terms of math that we did here ultimately all it is is writing out the full joint distribution and moving around the summations and discovering the structure of how can do calculations from the front and from the back to bring in to the time where we're at in a way that is not exponential in the number of variables we're considering it's linear every calculation is simple we do one simple calculation per time slides to work our way to time - all