On the Existence of Fixpoints in Moore's Autoepistemic Logic and the Non-Monotonic Logic of McDermott and Doyle

In [6] Moore has introduced a logic to represent the beliefs of ideal rational agents, called autoepistemic logic. This logic was presented as an improvement of the non-monotonic logic of McDermott and Doyle in [4]. We give a new method to characterize the fixpoints in both logics and thus obtain decision procedures for several problems in this context. Although the two logics are conceptually very different our method is very uniform.