  What constitutes jointly Poisson processes remains an unresolved issue. This
report reviews the current state of the theory and indicates how the accepted
but unproven model equals that resulting from the small time-interval limit of
jointly Bernoulli processes. One intriguing consequence of these models is that
jointly Poisson processes can only be positively correlated as measured by the
correlation coefficient defined by cumulants of the probability generating
functional.
