  (2) In conjunction with manifestations of FUNC, i.e. the Sum Rule and the Product Rule, QM yields constraints like VC1 or VC2 that contradict VD. So, providing concrete physical examples that could, given the Sum Rule and the Product Rule, instantiate VC1 or VC2 as just outlined is not enough. We must ask whether these rules themselves can be empirically supported. There was considerable discussion of this question in the early 80s — explicitly about whether the Sum Rule is empirically testable — and there was general agreement that it is  not.[15]