@incollection{GraedelOtto2014,
  booktitle = {Johan van Benthem on Logic and Information Dynamics},
  year = {2014},
  volume = {379},
  series = {Outstanding Contributions to Logic},
  author = {Gr{\"a}del, Erich and Otto, Martin},
  publisher = {Springer},
  editor = {Baltag, Alexandru and Smets, Sonja},
  pages = {3-31},
  title = {The freedoms of (guarded) bisimulation},
}