The argument x represents a fitted spatial point process model
  or a similar object.
is.stationary(x) returns TRUE if x represents
  a stationary point process, and FALSE if not.
is.poisson(x) returns TRUE if x represents
  a Poisson point process, and FALSE if not.
The functions is.stationary and is.poisson are generic,
  with methods for the classes "ppm" (Gibbs point process models),
  "kppm" (cluster or Cox point process models),
  "slrm" (spatial logistic regression models) and
  "rmhmodel" (model specifications for the
  Metropolis-Hastings algorithm).
  Additionally is.stationary has a method for
  classes "detpointprocfamily" and "dppm"
  (both determinantal point processes) and
  is.poisson has a method for 
  class "interact" (interaction structures for Gibbs models).
is.poisson.kppm will return FALSE, unless
  the model x is degenerate:
  either x has zero intensity so that its realisations are empty
  with probability 1, or it is a log-Gaussian Cox process
  where the log intensity has zero variance.
is.poisson.slrm will always return TRUE,
  by convention.