The Common Knowledge of Formula Exclusion
  For every set of primitive propositions and agents there is a canonical Kripke structure and a canonical map from any Kripke structure (defined with the same primitive propositions and agents) to this canonical one. A cell of the canonical Kripke structure is a set C such that if any agent considers a point x in C to be possible then all the other points considered possible by this agent are also in C. A cell C has finite fanout if at every point in C every agent considers possible only finitely many other points. We demonstrate a cell of this canonical Kripke structure such that every Kripke structure that maps to this cell does so surjectively, yet this cell does not have finite fanout. 
Robert Samuel Simon
math.LO