Combination of Upper and Lower Probabilities

In this paper, we consider several types of information and methods of combination associated with incomplete probabilistic systems. We discriminate between á priori' and evidential information. The former one is a description of the whole population, the latest is a restriction based on observations for a particular case. Then, we propose different combination methods for each one of them. We also consider conditioning as the heterogeneous combination of á priori' and evidential information. The evidential information is represented as a convex set of likelihood functions. These will have an associated possibility distribution with behavior according to classical Possibility Theory.