16 research outputs found

    Generalizing Newman’s Lemma for left-linear rewrite systems

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    Abstract. Confluence criteria for non-terminating rewrite systems are knowntoberareandnotoriouslydifficulttoobtain.Hereweprovea new result in this direction. Our main result is a generalized version of Newman’s Lemma for left-linear term rewriting systems that does not need a full termination assumption. We discuss its relationships to previous confluence criteria, its restrictions, examples of application as well as open problems. The whole approach is developed in the (more general) framework of context-sensitive rewriting which thus turns out to be useful also for ordinary (context-free) rewriting.

    Harnessing First Order Termination Provers Using Higher Order Dependency Pairs

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    Many functional programs and higher order term rewrite systems contain, besides higher order rules, also a significant first order part. We discuss how an automatic termination prover can split a rewrite system into a first order and a higher order part. The results are applicable to all common styles of higher order rewriting with simple types, although some dependency pair approach is needed to use them

    Complete Monotonic Semantic Path Orderings

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    Although theoretically it is very powerful, the semantic path ordering (SPO) is not so udeful in practice, since its monotonicity has to be proved by hand for each concrete term rewrite system (TRS). In this paper we present a monotonic variation of SPO, called MSPO. It characterizes termination, i.e. a TRS is terminating if and only if ist rules are included in some MSPO. Hence MSPO is a complete termination method. On the practical side, it can be easily automated using as ingredients standard interpretations and general-purpose ordering like RPO. This is shown to be a sufficiently powerful way to handeke several non-trivial examples and to obtain methods like dummy elimination or dependency pairs (without the dependency graph refinement) as particular cases. Finally, we obtain some positive modularity results for termination based on MSPO
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