 Vaidman 2012 uses symmetry to derive the Probability Postulate in another way. He starts from a situation which is symmetric in all relevant respects, so all outcomes must have equal probability. To derive the postulate, he assumes relativistic causality which tells us that the probability of an outcome of a measurement in one location cannot be affected by spatially remote manipulations, see McQueen and Vaidman 2019. Vaidman 2020 stresses, however, that relativistic causality of the evolution of the wave function of the Universe is not enough. In addition, we have to postulate the relativistic causality of the subjective experience of an observer within his world.