Let X be an event and IX an associated indicator random variable. IX is 1 if a value is in event X, 0 otherwise. Let Y be an event and IY the associated indicator random variable in the same way that IX is for event X. Let probabilities P(X) be denoted as p, P(Y) as q and the probability of the union X u Y be denoted as P(A u B) = r. Question: Find the expected value of the squared difference of IX and IY, in terms of p,q and r. That is, find E[(IX - IY)^2] in terms of p, q and r