approximation of the state that you use as your representation for state space and as a consequence first sort of assumptions might not exactly be true I think often it's dealt with in pretty much ad hoc way where people just look at the system and say ok for this system it seems like we need to look this far back or that far back to get what is effectively the state of the system by including enough history but I haven't seen like if necessarily like a very clear-cut way to define it in general and this ties directly on what we're