 An operation of change can raise or lower the position of a sentence in the ordering without affecting the belief set (but affecting how the belief state responds to new inputs). An operation of improvement, as proposed by Konieczny and Pérez (2008) increases the plausibility of a non-believed sentence \(p\) by moving some of the \(p\)-worlds to a higher position in the preference ordering of worlds. Even if such a change does not lead to \(p\) becoming a belief, its acceptance in later, additional operations can be facilitated. 