and so, \(B\) is not rational at \(v_2\) in \(w\) (note that \(u_B(o_4)=3&gt;1=u_B(o_2)\)). Stalnaker suggests that the players should be endowed with a belief revision policy that describes which informational state they would revert to in case they were to observe moves that are inconsistent with what they know about their opponents’ strategies. If \(B\) does learn that he can in fact move, then he has learned something about \(A\)’s strategy. In particular, he now knows that she cannot be following any strategy that prescribes that she chooses \(O_1\) at \(v_1\) (so, in particular, she cannot be following the strategy \(O_1I_3\).) Suppose that \(B\) is disposed to react to surprising information about \(A\)’s choice of strategy as follows: Upon learning that \(A\) is not following a strategy in which she chooses \(O_1\) at \(v_1\), he concludes that she is following strategy \(I_1O_3\). That is, \(B\)’s “belief revision policy” can be summarized as follows: If \(A\) makes one “irrational move”, then she will make another one. Stalnaker explains the apparent tension between this belief revision policy and his knowledge that if \(A\) where given the opportunity to choose at \(v_3\), then she would choose \(I_3\) as follows: