  In his famous thought experiment, Wigner assigns an entangled state to the
composite quantum system made up of Wigner's friend and her observed system.
While the two of them have different accounts of the process, each Wigner and
his friend can in principle verify his/her respective state assignments by
performing an appropriate measurement. As manifested through a click in a
detector or a specific position of the pointer, the outcomes of these
measurements can be regarded as reflecting directly observable "facts".
Reviewing arXiv:1507.05255, I will derive a no-go theorem for
observer-independent facts, which would be common both for Wigner and the
friend. I will then analyze this result in the context of a newly derived
theorem in arXiv:1604.07422, where Frauchiger and Renner prove that
"single-world interpretations of quantum theory cannot be self-consistent". It
is argued that "self-consistency" has the same implications as the assumption
that observational statements of different observers can be compared in a
single (and hence an observer-independent) theoretical framework. The latter,
however, may not be possible, if the statements are to be understood as
relational in the sense that their determinacy is relative to an observer.
