  Fourth, Howard's spatiotemporal separability condition (see section 4.3) requires that states of composite systems be determined by the states of their subsystems. In particular, spatiotemporal separability requires that joint probabilities of outcomes be determined as some function of the single probabilities of these outcomes. Winsberg and Fine (2003) object that as a separability condition, OI arbitrarily restricts this function to be a product function. And they argue that on a weakened formalization of separability, a violation of OI is compatible with separability. Fogel (2004) agrees that Winsberg and Fine's weakened formalization of separability is correct, but argues that, when supplemented by a certain ‘isotropy’ condition, OI implies this weakened separability condition. Fogel believes that his suggested ‘isotropy’ condition is very plausible, but, as he acknowledges, this condition involves a nontrivial measurement  context-independence.[33]