 Hard information flow, that is, the flow of information between the knowledge states of two or more agents, can be facilitated by more than one epistemic action. Two canonical examples are announcements and observations. When “announcement” is restricted to true and public announcement, its result on the receiving agent’s knowledge-base is similar to that of an observation (on the assumption that the agent believes the content of the announcement). The public announcement that \(\phi\) will restrict the model of the agent’s knowledge-base to the information states where \(\phi\) is true, hence “announce \(\phi\)” is an epistemic state transformer in the sense that it transforms the epistemic states of the agents in the group, (see van Ditmarsh, van der Hoek, and Kooi 2008:  74).[2] 