  In most classical models of belief change, epistemic states are represented
by theories (AGM) or formulas (Katsuno-Mendelzon) and the new pieces of
information by formulas. The Representation Theorem for revision operators says
that operators are represented by total preorders. This important
representation is exploited by Darwiche and Pearl to shift the notion of
epistemic state to a more abstract one, where the paradigm of epistemic state
is indeed that of a total preorder over interpretations. In this work, we
introduce a 3-valued logic where the formulas can be identified with a
generalisation of total preorders of three levels: a ranking function mapping
interpretations into the truth values. Then we analyse some sort of changes in
this kind of structures and give syntactical characterizations of them.
