  Assumption KS1 of the theorem obviously is an equivalent of VD. Assumptions KS2 (a) and (b) are called the Sum Rule and the Product Rule, respectively, in the literature. (The reader should again note that, in opposition to von Neumann’s implicit premise, these rules non-trivially relate the values of compatible observables only.) Both are consequences of a deeper principle called the functional composition principle (FUNC), which in turn is a consequence of (among other assumptions) NC. The connection between NC, FUNC, Sum Rule and Product Rule will be made explicit in Section 4.