filters which will essentially do sample based approximations to this entire calculation so they'll say I can't cover everything let me just run a particle filter which is much like the sampling based approaches to value iteration that we saw it's the counter part you just sample bunch of states look at the valuation update particle filters the equivalent you sample a bunch of possible states you don't know which ones correct you propagate them all re-weight them based on what are the evidence compatible with them or not and