  A general argument is presented against relativistic, unitary, single-outcome
quantum mechanics. This is achieved by combining the Wigner's Friend thought
experiment with measurements on a Greenberger-Horne-Zeilinger (GHZ) state, and
describing the evolution of the quantum state in various inertial frames.
Assuming unitary quantum mechanics and single outcomes, the result is that the
Born rule must be violated in some inertial frame: in that frame, outcomes are
obtained for which no corresponding term exists in the pre-measurement
wavefunction.
