  The purpose of this note is to give a generalization of Gleason's theorem
inspired by recent work in quantum information theory on "nonlocality without
entanglement." For multipartite quantum systems, each of dimension three or
greater, the only nonnegative frame functions over the set of unentangled
states are those given by the standard Born probability rule. However, if one
system is of dimension 2 this is not necessarily the case.
