 It is not our task to review here the various attempts to solve the above difficulties. One can find many exhaustive treatments of this problem in the literature. We conclude this section by discussing how the measurement problem is indeed a consequence of very general, in fact unavoidable, assumptions on the nature of measurements, and not specifically of the assumptions of von (oversimplified) von Neumann’s model. This was established in a series of theorems of increasing generality, notably the ones by Fine (1970), d’Espagnat (1971), Shimony (1974), Brown (1986) and Busch &amp; Shimony (1996). Possibly the most general and direct proof is given by Bassi and Ghirardi (2000), whose results we briefly summarize. The assumptions of the theorem are: