  A recent paper [1] argues that bipartite "PR-box" correlations, though
designed to respect relativistic causality, in fact violate relativistic
causality in the classical limit. As a test of Ref. [1], we consider GHZ
correlations as a tripartite version of PR-box correlations, and ask whether
the arguments of Ref. [1] extend to GHZ correlations. If they do - i.e. if they
show that GHZ correlations violate relativistic causality in the classical
limit - then Ref. [1] must be incorrect, since GHZ correlations are quantum
correlations and respect relativistic causality. But the arguments fail. We
also show that both PR-box correlations and GHZ correlations can be
retrocausal, but the retrocausality of PR-box correlations leads to
self-contradictory causal loops, while the retrocausality of GHZ correlations
does not.
