Retroactive Legal Changes and Revision Theory in Defeasible Logic

In earlier works, we used Defeasible Logic to argue that techniques from belief and base revision encounter a number of difficulties in modelling legal dynamics. In particular, we showed that these techniques are not suitable when legal changes are retroactive. This suggested to adopt a different logical model able to express two main timelines, one internal to a given temporal version of the legal system, and another relative to how the legal system evolves over time. In this paper, we adjust our view and show that, under some restrictions, ideas from base revision, if applied to Defeasible Logic or to similar rule-based systems, can indeed capture some significant aspects of annulments, abrogations, and derogations.