Extending the 2D Dependency Pair Framework for Conditional Term Rewriting Systems
Recently, a new dependency pair framework for proving operational termination of Conditional Term Rewriting Systems (CTRSs) has been introduced. We call it 2D Dependency Pair (DP) Framework for CTRSs because it makes explicit and exploits the bidimensional nature of the termination behavior of conditional rewriting, where rewriting steps \(s\rightarrow t\) and rewritings \(s\rightarrow ^*t\) (in zero or more steps) are defined for specific terms \(s\) and \(t\) by using an inference system where appropriate proof trees should be exhibited for such particular goals. In this setting, the horizontal component of the termination behavior concerns the existence of infinite sequences of rewriting steps, and the vertical component captures infinitely many climbs during the development of a proof tree for a single rewriting step. In this paper we extend the 2D DP Framework for CTRSs with several powerful processors for proving and disproving operational termination that specifically exploit the structure of conditional rules. We provide the first implementation of the 2D DP Framework as part of the termination tool mu-term. Our benchmarks suggest that, with our new processors, the 2D DP Framework is currently the most powerful technique for proving operational termination of CTRSs.
KeywordsConditional rewriting Dependency pairs Operational termination Program analysis
We thank the referees for their comments and suggestions.