 An autoepistemic theory consists of the beliefs of an agent including her reflective beliefs about her beliefs. For the latter an autoepistemic belief operator \(\mathsf{B}\) is used. In our example such a theory may contain \(\neg \mathsf{B} \mathit{brother} \supset \neg \mathit{brother}\). Autoepistemic logic specifies ideal properties of such theories. Following  Stalnaker (1993),  an autoepistemic theory \(\Gamma\) should be stable: 