 Dempster-Shafer (DS) belief functions (Dempster 1968, Shafer 1976) can also be understood as an attempt to formally distinguish risk from ambiguity. Like probability functions, DS belief functions are real-valued functions \( \Bel: \mathbf{A} \rightarrow \Re\) satisfying Positivity and Unitarity. But whereas probability functions are additive, DS belief functions are only Super-additive, i.e., for all propositions \(A, B\) in \(\mathbf{A}\):