The closure of the set of entropy functions associated with n discrete variables, Gammar*n, is a convex cone in (2n-1)- dimensional space, but its full characterization remains an open problem. In this paper, we map Gammar*n to an n-dimensional regio
n Phi*n by averaging the joint entropies with the same number of variables, and show that the simpler Phi*n can be characterized solely by the Shannon-type information inequalities
