@INPROCEEDINGS{AcetoEtAl11,
  author = 	 {Luca Aceto and Ignacio F\'abregas and de Frutos Escrig, David 
                  and Anna Ing\'olfsd\'ottir and Miguel Palomino},
  title = 	 {Graphical representation of covariant-contravariant
                  modal formulas},
  editor =       {Bas Luttik and Frank Valencia},
  booktitle =    {Proceedings 18th International Workshop on Expressiveness in 
                  Concurrency, Aachen, Germany, 5th September 2011},
  series =       {Electronic Proceedings in Theoretical Computer Science},
  volume =       64,
  pages =        {1-15},
  year =         2011
}