A Multiple-Valued Logical Semantics for Prolog

Abs t rac t . The coincidence of the declarative and procedural interpretations of logic programs does not apply to Prolog programs, due to the depth-first left-to-right evaluation strategy of Prolog interpreters. We propose a new semantics for Prolog programs based on a new fourvalued logic. The semantics is based on a new concept of completion analogous to Clark's and it enjoys the nice properties of the declarative semantics of logic programming: existence of the minimal Herbrand model, equivalence of the model-theoretic and operational semantics.