Update postulates without inertia
Résumé
Starting from Katsuno and Mendelzon postulates, a new set of postulates which is minimal and complete has been defined, these postulates characterize an update operator. The update operator class which is obtained is larger than Katsuno and Mendelzon's one, since it includes updating operators which are not inert, and which allow for the existence of unreachable states. The main property is that every update operator satisfying this new set of postulates admits an underlying ranked transition graph. The rank-ordering of its transitions has not to be faithful as in Katsuno and Mendelzon system.