 The propositional account provides an intuitively clear picture of some aspects of belief change. It is convenient to use a geometrical surface to represent the set of possible worlds. In Diagram 1, every point on the rectangle’s surface represents a possible world. The circle marked \([K]\) represents those possible worlds in which all sentences in \(K\) are true, i.e., the set \([K]\) of possible worlds. The area marked \([p]\) represents those possible worlds in which the sentence \(p\) is true.