On Deducing Conditional Independence from d-Separation in Causal Graphs
  with Feedback (Research Note)
  Pearl and Dechter (1996) claimed that the d-separation criterion for
conditional independence in acyclic causal networks also applies to networks of
discrete variables that have feedback cycles, provided that the variables of
the system are uniquely determined by the random disturbances. I show by
example that this is not true in general. Some condition stronger than
uniqueness is needed, such as the existence of a causal dynamics guaranteed to
lead to the unique solution.
