@Inproceedings{EPTCS64.1,
  author    = {Aceto, Luca and F\'abregas, Ignacio and Frutos-Escrig, David de and Ing\'olfsd\'ottir, Anna and Palomino, Miguel},
  year      = {2011},
  title     = {Graphical representation of covariant-contravariant modal formulae},
  editor    = {Luttik, Bas and Valencia, Frank},
  booktitle = {{\rm Proceedings 18th International Workshop on}
               Expressiveness in Concurrency,
               {\rm Aachen, Germany, 5th September 2011}},
  series    = {Electronic Proceedings in Theoretical Computer Science},
  volume    = {64},
  publisher = {Open Publishing Association},
  pages     = {1-15},
  doi       = {10.4204/EPTCS.64.1},
}