@TechReport{KKLW07,
  author =	 "Joost-Pieter Katoen, Daniel Klink, Martin Leucker, Verena Wolf",
  title =	 "Three-Valued Abstraction for Probabilistic Systems",
  institution =	 "RWTH Aachen",
  year =	 "2007",
  number =	 "AIB-2007-20",
  month =	 dec,
  url =          "http://aib.informatik.rwth-aachen.de/2007/2007-20.ps.gz",
}