Suppose Di is an observed binary variable equal to one if an individual is assigned to treat- ment and equal to zero otherwise. Further, suppose Y; is an observed variable measuring some outcome of interest, that is hypothesized to be affected by Di. Recall that we express Y in terms of the potential outcomes Yli and You as Yi Yli if Di = 1 You if Di = 0 This means that if Di = 0, we observe You, while Y1; is the unobserved counterfactual outcome. Similarly, if Di = 1, we observe Yui, while You is the unobserved counterfactual outcome. (6.1) Write down a single equation for Yi in terms of Yli, You, and Di