Tabling, Rational Terms, and Coinduction Finally Together!

Tabling is a commonly used technique in logic programming for avoiding cyclic behavior of logic programs and enabling more declarative program de nitions. Furthermore, tabling often improves computational performance. Rational term are terms with one or more in nite subterms but with a nite representation. Rational terms can be generated in Prolog by omitting the occurs check when unifying two terms. Applications of rational terms include de nite clause grammars, constraint handling systems, and coinduction. In this paper, we report our extension of YAP's Prolog tabling mechanism to support rational terms. We describe the internal representation of rational terms within the table space and prove its correctness. We then use this extension to implement a tabling based approach to coinduction. We compare our approach with current coinductive transformations and describe the implementation. In addition, we present an algorithm that ensures a canonical representation for rational terms.