version of this extended abstract appeared in the proceedings of the Ninth European Conference on Symbolic and Quantitative Approaches to Reasoning with Uncertainty (ECSQARU-07), Hammamet, Tunisia, 2007 (LNAI 4724, pp. 548-559). The first author was (partly) supported by the Netherlands Organisation for Scientific Research (NWO).
Johan Kwisthout, Hans L. Bodlaender, Gerard Tel