  Evidential reasoning is now a leading topic in Artificial Intelligence.
Evidence is represented by a variety of evidential functions. Evidential
reasoning is carried out by certain kinds of fundamental operation on these
functions. This paper discusses two of the basic operations on evidential
functions, the discount operation and the well-known orthogonal sum operation.
We show that the discount operation is not commutative with the orthogonal sum
operation, and derive expressions for the two operations applied to the various
evidential function.
