This heuristic need the parameters inside score_to_probabilities(). The implementation is easy but I need to talk to you and Sergey about how to modify that function if we decide to have the softmax heuristic. Please take a look at Eq.(7) in http://hal.archives-ouvertes.fr/docs/00/10/39/55/PDF/cr102875872670.pdf, maybe I am wrong and there is an easier way to do. Let's discuss on IRC if necessary.