@article{MoellerStruth2006,
  author    = {Bernhard M{\"o}ller and Georg Struth},
  title     = {Algebras of modal operators and partial correctness},
  journal   = {Theoretical Computer Science},
  volume    = {351},
  number    = {2},
  pages     = {221 -- 239},
  doi       = {10.1016/j.tcs.2005.09.069},
  year      = {2006},
}