 informally read, “p is true but agent a does not believe it”. Let us suppose that this formula is true; that is, p is true and, indeed, agent a does not believe that p is true. Now suppose that agent a receives the formula \eqref{MF} from a completely trustworthy source and is supposed to change her beliefs to take into account the information this formula provides. In a dynamic belief change, she will accept the formula \eqref{MF} and hence, in particular, she will come to believe that p is true. But then the formula \eqref{MF} becomes false: she now believes p and therefore the formula \(\lnot[a]p\) (“agent a does not believe p”) is false. So we see that this belief change is indeed dynamic: in revising her beliefs based on the incoming true formula \eqref{MF}, the truth of the formula \eqref{MF} was itself changed. That is, the “situation”, which involves the truth of p and the agent’s beliefs about this truth, changed as per the belief change brought about by the agent learning that \eqref{MF} is true. (As an aside, this example shows that for dynamic belief change, the AGM Success postulate is violated and so must be dropped.) 