@article{SVW09:sacs,
  author = {Sokolova, A. and Vink, E.P. de and Woracek, H.},
  title = { Coalgebraic weak bisimulation for action-type systems },
  journal = {Scientific Annals of Computer Science},
  volume = {19},
  pages = {93--144}
  year = {2009}
}