AVACS – Automatic Verification and Analysis of Complex Systems REPORTS of SFB/TR 14 AVACS Editors: Boardof SFB/TR 14 AVACS Minimal Counterexamples for Refuting ω-Regular Properties of Markov Decision Processes – Extended Version – by Ralf Wimmer Nils Jansen Erika ´ Abrah´ am Joost-Pieter Katoen Bernd Becker AVACS Technical ReportNo. 88 September 2012 ISSN: 1860-9821