Multiple choice
In the E91 protocol the correlation for measurement angles x and y on a singlet is E(x,y) = -cos(x - y). Using Alice's angles a = 0, a' = pi/2 and Bob's angles b = pi/4, b' = 3pi/4, the CHSH quantity is S = E(a,b) - E(a,b') + E(a',b) + E(a',b'). What is |S|?