in their seminal 1994 paper, popescu and rorhlich explore whether quantum correlations can be explained by appealing to relativistic causality alone. namely, whether any hypothetical box formula_145 would allow building a device capable of transmitting information faster than the speed of light. at the level of correlations between two parties, einstein’s causality translates in the requirement that alice’s measurement choice should not affect bob’s statistics, and viceversa. otherwise, alice (bob) could signal bob (alice) instantaneously by choosing her (his) measurement setting formula_29 formula_147 appropriately. mathematically, popescu and rohrlich’s no-signalling conditions are: