@article {DBLP:journals/jlp/BarbutiMPT90, title = {A Transformational Approach to Negation in Logic Programming}, journal = {J. Log. Program.}, volume = {8}, number = {3}, year = {1990}, pages = {201-228}, author = {Roberto Barbuti and Paolo Mancarella and Dino Pedreschi and Franco Turini} }