 Various modal semantics have been proposed for autoepistemic logic (see the entry on  modal logic  for more background on modal logics). For instance,  Moore (1984)  proposes an S5-based Kripkean possible world semantics and  Lin and Shoham (1990)  propose bi-modal preferential semantics (see Section  Selection semantics  below) for both autoepistemic logic and default logic. In  Konolige (1988)  it has been observed that the fixed point characterization of stable expansions can be alternatively phrased only on the basis of the set of formulas \(\Gamma_0\) in \(\Gamma\) that do not contain occurrences of the modal operator \(\mathsf{B}\): 