  Frauchiger and Renner (2018) initiated the discussion of scenarios of this sort involving more than two observers, which have come to be called “extended Wigner’s friend” scenarios. Further results along these lines include Brukner (2018), Bong et al. (2020), and Guérin et al. (2021). The strategy of these investigations is to present some set of plausible-seeming assumptions (a different set, for each of the works cited), and to show, via consideration of a hypothetical situation involving multiple observers, the inconsistency of that set of assumptions. The theorems are, therefore, no-go theorems for approaches to the measurement problem that would seek to satisfy all of the members of the set of assumptions that has been shown to be inconsistent.