Paola Bruscoli Francesca Levi Giorgio Levi Maria Chiara Meo Compilative Constructive Negation in Constraint Logic Programs. 52-67 1994 conf/caap/1994 CAAP db/conf/caap/caap94.html#BruscoliLLM94 http://dx.doi.org/10.1007/BFb0017473