“…is smooth over t. Furthermore the smoothness assumption on Z t−1 and Z t−1 (U it ) over t is required for us and but NOT for required for Gagliardini, Ossola, and Scaillet (2019). However, the structure in Equation (1.5) is not necessary for us, therefore there exist models where we can cover but not covered by Gagliardini, Ossola, and Scaillet (2019). For example if we set, β t is a vector of β it .…”