“…2.2. Because the models in could have any LTI structures , and are generally defined in impulse response forms as in the succeeding text: where and are Markov parameters of and , respectively. Definition A quasi‐stationary data set Z ∞ = { y 1 , u 1 , ⋯ , y k , u k , ⋯ } is informative if for any two pairs of models …”