  We are given k points (events) in (n+1)-dimensional Minkowski space. Using
the theory of hyperplane arrangments and chromatic polynomials, we obtain
information the number of different orders in which the events can occur in
different reference frames if the events are sufficiently generic. We consider
the question of what sets of orderings of the points are possible and show a
connection with sphere orders and the allowable sequences of Goodman and
Pollack.
