 for each \(A \in \mathbf{A}\). In other words: a set of worlds is only as disbelieved as its most plausible member. By convention, we set \(\varrho(\varnothing)=\infty\). This entails that ranking functions are (finitely) minimitive and hence super-additive. In other words, for all \(A, B\) in \(\mathbf{A}\),