Let X1 and X2 be random variables with support S1 = {0, 1} and
S2 = {−1, 1},
respectively, and with the joint pdf f(x1, x2) such that f(0,
−1) = 1/3, f(0, 1) = 1/3, f(1, −1) = 1/6 and f(1, 1) =