  Bell's theorem revealed that a local hidden-variable model cannot completely
reproduce the quantum mechanical predictions. Bell's inequality provides an
upper bound under the locality and reality assumptions that can be violated by
correlated measurement statistics of quantum mechanics. Greenberger, Horne, and
Zeilinger (GHZ) gave a more compelling proof of Bell's theorem without
inequalities by considering perfect correlations rather than statistical
correlations. This work presents a temporal analog of the GHZ argument that
establishes Bell's theorem in time without inequalities.
