The present paper is structured around two main constructions, fixed points of functors and fibrations and sections of functors. Fixed points of functors are utilized to resolve problems of infinite regress that have recently appeared in economics. Fibrations and sections are utilized to model...

We observe that the set of all priors of an agent is the convex hull of his types. A prior common to all agents exists, if the sets of the agents' priors have a point in common. We give a necessary and sufficient condition for the non-emptiness of the intersection of several closed convex...