@Unpublished{DJN96:manuscript,
  author = 	 {Stefan Dziembowski and Marcin Jurdzi{\'n}ski and 
                  Damian Niwi{\'n}ski},
  title = 	 {On the Expression Complexity of the Modal 
                  $\mu$-Calculus Model Checking},
  note = 	 {Unpublished manuscript},
  address =      {Instytut Informatyki, Uniwersytet Warszawski,
                  Warszawa, Poland}
  year = 	 1996,
  month = 	 nov
}