In the context of logic program updates, a knowledge base, which is presented as a logic program, can be updated in terms of another logic program, i.e. a set of update rules. In this paper, we investigate the complexity of logic program updates where conflict resolution on defeasible information is explicitly taken into account in an update. We show that in general the problem of model checking in logic program updates is co-NP-complete, and the corresponding inference problem is Π_2~p-complete. We also characterize particular classes of update specifications where the inference problem has a lower computational complexity. These results confirm that logic program update, even if with the issue of conflict resolution on defeasible information to be presented, is not harder than the principal update tasks.
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