NoteComparison of information structures in zero-sum games

This note provides simple necessary and sufficient conditions for the comparison of information structures in zero-sum games. This solves an open problem of Grossner and Mertens [Gossner, O., Mertens, J.-F., 2001. The value of information in zero-sum games. http://ogossner.free.fr/Articles/abstract.pdf]. The conditions are phrased in terms of Blackwell garbling of information of each of the players.