 The Public Announcement Closure Theorem tells us that reflexivity, transitivity, and Euclideanness are always closed under the public announcement operation. Seriality is in general not; however, if seriality comes with Euclideanness, then public announcements of formulas of the form \(F\land\bigwedge_{x\in\sA}\may{x} F\) (read, “F is true and consistent with each agent’s knowledge”) preserve both seriality and Euclideanness. Therefore, if we wish to study classes of models that are serial, then, to make use of the above theorem, we will need to further restrict to models that are both serial and Euclidean and we will need to restrict the language of public announcements so that all announcement formulas have this form. (One could also restrict to another form, so long as public announcements of this form preserve seriality over some class \(\sC\) of serial models.) Restricting the language \eqref{PAL} by requiring that public announcements have the form \(F\land\bigwedge_{x\in\sA}\may{x} F\) leads to the language \eqref{sPAL} of serial Public Announcement Logic, which we may use when interested in serial and Euclidean Kripke models. 