Suppose that \(C\) is true. Then, Ann does believe that Bob’s assumption is wrong, and, by introspection, she believes that she believes this. That is to say, Ann believes that \(C\) is correct. Furthermore, according to (S), Ann believes that Bob’s assumption is \(C\). So, Ann, in fact, believes that Bob’s assumption is correct (she believes Bob’s assumption is \(C\) and that \(C\) is correct). So, \(C\) is false.