Independence gives EE(Z)=∑z,yF(y,z)P(Y=y)P(Z=z)=EF(Y,Z). Moreover, EV(Z)=E(F(Y,Z)2)−E(E(Z)2), while VarE(Z)=E(E(Z)2)−(EF(Y,Z))2. Adding proves the law of total variance
For one Bernoulli variable, direct expansion gives VarF(X1)=p(1−p)(F(1)−F(0))2. Applying the law of total variance successively to the coordinates gives the variance tensorization