 Clearly, there is no stable theory that is grounded in \(\Xi_1\) and that contains \(\mathit{brother}\) and/or \(\mathsf{B} \mathit{brother}\) like our \(\Gamma_1\) above. The reason is that we fail to derive \(\mathit{brother}\) from \(\Xi_1 \cup \{\mathsf{B} \psi \mid \psi \in \Gamma_1\} \cup \{\neg \mathsf{B} \psi \mid \psi \notin \Gamma_1\}\). The only stable extension of \(\Xi_1\) contains \(\neg \mathsf{B} \mathit{brother}\) and \(\neg \mathit{brother}\). 