  Proven-in-use arguments are needed when pre-developed products with an
in-service history are to be used in different environments than those they
were originally developed for. A product may include software modules or may be
stand-alone integrated hardware and software modules.The topic itself is not
new, but most recent approaches have been based on elementary probability such
as urn models which lead to very restrictive requirements for the system or
software to which it has been applied.
  The aim of this paper is to base the argumentation on a general probabilistic
model based on Grigelionis or Palm Khintchine theorems, so that the results can
be applied to a very general class of products without unnecessary limitations.
The advantage of such an approach is also that the same requirements hold for a
broad class of products.
