  This paper shows that a necessary condition for regular identification of the OLIVA is also sufficient for  existence of an IV estimand in a linear IV model.
<clarity>   This paper shows that a necessary condition for regular identification of the OLIVA is also sufficient for  existence of an IV estimand in a linear IV model.
 This paper shows that a necessary condition for standard inference on the OLIVA is also sufficient for existence of an IV estimand in a linear IV model.