Update, the Infinite Case
Carlos Areces, Verónica Becher · 1999
We provide a set of postulates that characterizes Katsuno and Men-delzon’s update operation [3] for a possibly infinite propositional lan-guage. In this way we extend their original operator which was only defined for finite languages. After reformulating the update operation as a function on theories, we show that Katsuno and Mendelzon’s orig-inal postulates are not sufficient to provide a characterization theorem. A strengthening of postulate (U8) is needed for a representation result. The new definition of update on (possibly infinite) languages puts the two main notions of theory change (update and revision) in the same ground and opens the way to a better comparison of their prop-erties.