 The definition of progress by RP can be contrasted with the model of belief revision (Gärdenfors, 1988). The simplest case of revision is expansion: a theory \(T\) is conjoined by an input statement \(A\), so that the new theory is \(T \amp A\). According to the min-sum measure, if \(T\) and \(A\) are true, then the expansion \(T \amp A\) is at least as truthlike as \(T\). But if \(T\) is false and \(A\) is true, then \(T \amp A\) may be less truthlike than \(T\). For example, let the false theory \(T\) state that the number of planets is 9 or 20, and let \(A\) be the true sentence that this number is 8 or 20. Then \(T \amp A\) states that the number of planets is 20, but this is clearly less truthlike than \(T\) itself. Similar examples show that the AGM revision of a false theory by true input need not increase truthlikeness (Niiniluoto 2011).