A Gleason-type theorem for any dimension based on a gambling formulation   of Quantum Mechanics
  Based on a gambling formulation of quantum mechanics, we derive a Gleason-type theorem that holds for any dimension n of a quantum system, and in particular for n = 2. The theorem states that the only logically consistent probability assignments are exactly the ones that are definable as the trace of the product of a projector and a density matrix operator. In addition, we detail the reason why dispersion-free probabilities are actually not valid, or rational, probabilities for quantum mechanics, and hence should be excluded from consideration. 
Alessio Benavoli, Alessandro Facchini, Marco Zaffalon
quant-ph math.PR