@InProceedings{progress03,
  author = 	 {A. Sokolova and Vink, E.P. de},
  title = 	 {On Relational Properties of Lumpability},
  booktitle = 	 {Proc. PROGRESS Workshop 2003},
  pages =	 {6pp},
  year =	 2003,
  publisher =	 {STW, Utrecht}
}