The freeze out (FO) of the expanding systems, created in relativistic heavy
ion collisions, is discussed. We start with kinetic FO model, which realizes
complete physical FO in a layer of given thickness, and then combine our
gradual FO equations with Bjorken type system expansion into a unified model.
We shall see that the basic FO features, pointed out in the earlier works, are
not smeared out by the expansion.Comment: 3 pages, 2 figure