@INPROCEEDINGS{AmatoL97,
  author = {Gianluca Amato and Giorgio Levi},
  title = {Properties of the lattice of observables in logic programming},
  booktitle = {1997 Joint Conf. on Declarative Programming, APPIA-GULP-PRODE'97,
        Grado, Italy, June 16-19, 1997},
  year = {1997},
  editor = {Moreno Falaschi and Marisa Navarro and Alberto Policriti},
  pages = {175--187},
  address = {Grado, Italy},
  month = jun
}