@conference {DBLP:conf/deductive/CorciuloGPZ94, title = {Expressive Power of Non-Deterministic Operators for Logic-based Languages}, booktitle = {Workshop on Deductive Databases and Logic Programming}, year = {1994}, pages = {27-40}, author = {Luca Corciulo and Fosca Giannotti and Dino Pedreschi and Carlo Zaniolo} }