the new variable condition all variables you already have but in this model we have a conditional independence we don't need a condition on the past observations if we have the current state and so that's why we just have XT plus 1 here and not XT plus 1 and all observations to condition on because once we know XT plus 1 those past observations don't need to be conditioned on anymore they're independent of Z T plus 1 and that's shown in the graph structure here and we're looking at we're getting z2 given everything in the past is the same thing