@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} } @conference {DBLP:conf/tapsoft/BarbutiMPT87, title = {Intensional Negation of Logic Programs: Examples and Implementation Techniques}, booktitle = {TAPSOFT, Vol.2}, year = {1987}, pages = {96-110}, author = {Roberto Barbuti and Paolo Mancarella and Dino Pedreschi and Franco Turini} }