Update, the innite case
Carlos Areces, TV Amsterdam, Buenos Aires · 1999
We provide a set of postulates that characterizes Katsuno and Mendelzon’s update operation [3] for a possibly innite propositional language. In this way we extend their original operator which was only dened for nite languages. After reformulating the update operation as a function on theories, we show that Katsuno and Mendelzon’s original postulates are not sucient to provide a characterization theorem. A strengthening of postulate (U8) is needed for a representation result. The new denition of update on (possibly innite) 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 properties.