High Quality Content by WIKIPEDIA articles! The Wigner - d'Espagnat inequality is a basic result of set theory. It is named for Eugene Wigner and Bernard d'Espagnat who (as pointed out by Bell) both employed it in their popularizations of quantum mechanics.Accordingly, the ratios N obtained by A, B, and C, with the particular constraints on their setup in terms of values of orientation angles, cannot have been derived all at once, in one and the same set of trials together; otherwise they'd necessarily satisfy the Wigner - d'Espagnat inequalities. Instead, they had to be derived in three distinct sets of trials, separately and pairwise by A and B, by A and C, and by B and C, respectively.