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14
Termination of Term Rewriting Using Dependency Pairs
 Comput. Sci
, 2000
"... We present techniques to prove termination and innermost termination of term rewriting systems automatically. In contrast to previous approaches, we do not compare left and righthand sides of rewrite rules, but introduce the notion of dependency pairs to compare lefthand sides with special subter ..."
Abstract

Cited by 214 (46 self)
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We present techniques to prove termination and innermost termination of term rewriting systems automatically. In contrast to previous approaches, we do not compare left and righthand sides of rewrite rules, but introduce the notion of dependency pairs to compare lefthand sides with special subterms of the righthand sides. This results in a technique which allows to apply existing methods for automated termination proofs to term rewriting systems where they failed up to now. In particular, there are numerous term rewriting systems where a direct termination proof with simplification orderings is not possible, but in combination with our technique, wellknown simplification orderings (such as the recursive path ordering, polynomial orderings, or the KnuthBendix ordering) can now be used to prove termination automatically. Unlike previous methods, our technique for proving innermost termination automatically can also be applied to prove innermost termination of term rewriting systems that are not terminating. Moreover, as innermost termination implies termination for certain classes of term rewriting systems, this technique can also be used for termination proofs of such systems.
Natural termination
 Theoretical Computer Science
"... Abstract. We generalize the various path orderings and the conditions under which they work, and describe an implementation of this general ordering. We look at methods for proving termination of orthogonal systems and give a new solution to a problem of Zantema's. 1 ..."
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Cited by 83 (11 self)
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Abstract. We generalize the various path orderings and the conditions under which they work, and describe an implementation of this general ordering. We look at methods for proving termination of orthogonal systems and give a new solution to a problem of Zantema's. 1
Automatically Proving Termination Where Simplification Orderings Fail
, 1997
"... To prove termination of term rewriting systems (TRSs), several methods have been developed to synthesize suitable wellfounded orderings automatically. However, virtually all orderings that are amenable to automation are socalled simplification orderings. Unfortunately, there exist numerous interes ..."
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Cited by 32 (9 self)
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To prove termination of term rewriting systems (TRSs), several methods have been developed to synthesize suitable wellfounded orderings automatically. However, virtually all orderings that are amenable to automation are socalled simplification orderings. Unfortunately, there exist numerous interesting and relevant TRSs that cannot be oriented by orderings of this restricted class and therefore their termination cannot be proved automatically with the existing techniques. In this paper we present a new automatic approach which allows to apply the standard techniques for automated termination proofs to those TRSs where these techniques failed up to now. For that purpose we have developed a procedure which, given a TRS, generates a set of inequalities (constraints) automatically. If there exists a wellfounded ordering satisfying these constraints, then the TRS is terminating. It turns out that for many TRSs where a direct application of standard techniques fails, these standard techniq...
Proving Innermost Normalisation Automatically
, 1997
"... We present a technique to prove innermost normalisation of term rewriting systems (TRSs) automatically. In contrast to previous methods, our technique is able to prove innermost normalisation of TRSs that are not terminating. Our technique can also be used for termination proofs of all TRSs where in ..."
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Cited by 28 (11 self)
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We present a technique to prove innermost normalisation of term rewriting systems (TRSs) automatically. In contrast to previous methods, our technique is able to prove innermost normalisation of TRSs that are not terminating. Our technique can also be used for termination proofs of all TRSs where innermost normalisation implies termination, such as nonoverlapping TRSs or locally confluent overlay systems. In this way, termination of many (also nonsimply terminating) TRSs can be verified automatically. 1. Introduction Innermost rewriting, i.e. rewriting where only innermost redexes are contracted, can be used to model callbyvalue computation semantics. For that reason, there has been an increasing interest in innermost normalisation (also called innermost termination), i.e. in proving that the length of every innermost reduction is finite. Techniques for proving innermost normalisation can for example be utilized for termination proofs of functional programs (modelled by TRSs) or o...
Type inference and semiunification
 In Proceedings of the ACM Conference on LISP and Functional Programming (LFP ) (Snowbird
, 1988
"... In the last ten years declarationfree programming languages with a polymorphic typing discipline (ML, B) have been developed to approximate the flexibility and conciseness of dynamically typed languages (LISP, SETL) while retaining the safety and execution efficiency of conventional statically type ..."
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Cited by 25 (6 self)
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In the last ten years declarationfree programming languages with a polymorphic typing discipline (ML, B) have been developed to approximate the flexibility and conciseness of dynamically typed languages (LISP, SETL) while retaining the safety and execution efficiency of conventional statically typed languages (Algol68, Pascal). These polymorphic languages can be type checked at compile time, yet allow functions whose arguments range over a variety of types. We investigate several polymorphic type systems, the most powerful of which, termed MilnerMycroft Calculus, extends the socalled letpolymorphism found in, e.g., ML with a polymorphic typing rule for recursive definitions. We show that semiunification, the problem of solving inequalities over firstorder terms, characterizes type checking in the MilnerMycroft Calculus to polynomial time, even in the restricted case where nested definitions are disallowed. This permits us to extend some infeasibility results for related combinatorial problems to type inference and to correct several claims and statements in the literature. We prove the existence of unique most general solutions of term inequalities, called most general semiunifiers, and present an algorithm for computing them that terminates for all known inputs due to a novel “extended occurs check”. We conjecture this algorithm to be
Matchbounded string rewriting
 Applicable Algebra in Engineering, Communication and Computing
"... ..."
Deciding Innermost Loops
 PROC. RTA '08
, 2008
"... We present the first method to disprove innermost termination of term rewrite systems automatically. To this end, we first develop a suitable notion of an innermost loop. Second, we show how to detect innermost loops: One can start with any technique amenable to find loops. Then our novel procedur ..."
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Cited by 4 (4 self)
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We present the first method to disprove innermost termination of term rewrite systems automatically. To this end, we first develop a suitable notion of an innermost loop. Second, we show how to detect innermost loops: One can start with any technique amenable to find loops. Then our novel procedure can be applied to decide whether a given loop is an innermost loop. We implemented and successfully evaluated our method in the termination prover AProVE.
C.: Loops under Strategies
 Proc. of the 20th International Conference on Rewriting Techniques and Applications, RTA’09. LNCS
, 2009
"... Abstract. Most techniques to automatically disprove termination of term rewrite systems search for a loop. Whereas a loop implies nontermination for full rewriting, this is not necessarily the case if one considers rewriting under strategies. Therefore, in this paper we first generalize the notion o ..."
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Cited by 2 (1 self)
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Abstract. Most techniques to automatically disprove termination of term rewrite systems search for a loop. Whereas a loop implies nontermination for full rewriting, this is not necessarily the case if one considers rewriting under strategies. Therefore, in this paper we first generalize the notion of a loop to a loop under a given strategy. In a second step we present two novel decision procedures to check whether a given loop is a contextsensitive or an outermost loop. We implemented and successfully evaluated our method in the termination prover T T T 2. 1
René Thiemann ∗ Loops under Strategies... Continued
"... While there are many approaches for automatically proving termination of term rewrite systems, up to now there exist only few techniques to disprove their termination automatically. Almost all of these techniques try to find loops, where the existence of a loop implies nontermination of the rewrite ..."
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While there are many approaches for automatically proving termination of term rewrite systems, up to now there exist only few techniques to disprove their termination automatically. Almost all of these techniques try to find loops, where the existence of a loop implies nontermination of the rewrite system. However, most programming languages use specific evaluation strategies, whereas loop detection techniques usually do not take strategies into account. So even if a rewrite system has a loop, it may still be terminating under certain strategies. Therefore, our goal is to develop decision procedures which can determine whether a given loop is also a loop under the respective evaluation strategy. In earlier work, such procedures were presented for the strategies of innermost, outermost, and contextsensitive evaluation. In the current paper, we build upon this work and develop such decision procedures for important strategies like leftmostinnermost, leftmostoutermost, (max)parallelinnermost, (max)paralleloutermost, and forbidden patterns (which generalize innermost, outermost, and contextsensitive strategies). In this way, we obtain the first approach to disprove termination under these strategies automatically. 1