Characterizability in Belief Revision

For instance, does it form a "nice" class, which can be characterized A formal framework is given for the postulate characterizability by postulates? of a class of belief revision operators, Proving non-characterizability presupposes a formal definition obtained from a class of partial preorders using of a postulate. However, as noted in the survey [Fermé minimization. It is shown that for classes of posets and Hansson, 2011] characterizability is equivalent to a special kind of "theories of belief change developed in the AGM definability in monadic second-order logic, which tradition are not logics in a strict sense, but rather turns out to be incomparable to first-order definability.