Revision of Defeasible Logic Preferences

There are several contexts of non-monotonic reasoning where a prior7 ity between rules is established whose purpose is preventing conflicts. 8 One formalism that has been widely employed for non-monotonic reasoning is 9 the sceptical one known as Defeasible Logic. In Defeasible Logic the tool used 10 for conflict resolution is a preference relation between rules, that establishes the 11 priority among them. 12 In this paper we investigate how to modify such a preference relation in a de13 feasible logic theory in order to change the conclusions of the theory itself. We 14 argue that the approach we adopt is applicable to legal reasoning where users, in 15 general, cannot change facts or rules, but can propose their preferences about the 16 relative strength of the rules. 17 We provide a comprehensive study of the possible combinatorial cases and we 18 identify and analyse the cases where the revision process is successful. 19 After this analysis, we identify three revision/update operators and study them 20 against the AGM postulates for belief revision operators, to discover that only a 21 part of these postulates are satisfied by the three operators. 22