@InProceedings{BKH99,
  author = 	 {C. Baier and J.-P.~Katoen and H.~Hermanns},
  title = 	 {Approximate Symbolic Model Checking of Continuous-Time Markov
      Chains},
  booktitle = 	 {Proc. 10th International Conference on Concurrency
      Theory (CONCUR'99)},
  pages =	 {146-161},
  year =	 1999,
  volume =	 1664,
  series =	 {Lecture Notes in Computer Science}
}