Reasoning About Permitted Announcements

We formalize what it means to have permission to say something. We adapt the dynamic logic of permission by van der Meyden [22] to the case where atomic actions are public truthful announcements. We also add a notion of obligation. Our logic is an extension of the logic of public announcements introduced by Plaza [17] with dynamic modal operators for permission and for obligation. We axiomatize the logic and show that it is decidable.