  We present a discussion of the extended Wigner's friend thought experiment
proposed by Frauchiger and Renner in [1]. We show by using various arguments,
including textbook quantum mechanics and the ontological approach of Contexts,
Systems, Modalities (CSM), that no contradiction arises if one admits that
agents must agree on what is considered as a system and what is not. In such a
contextually objective approach of quantum mechanics, the apparent
contradiction is automatically removed. We also discuss why this mutual
agreement between agents is already implicit in the standard formulations of
quantum mechanics, and why removing it leads to inconsistencies.
