99 research outputs found
Formalizing Knuth-Bendix Orders and Knuth-Bendix Completion
We present extensions of our Isabelle Formalization of Rewriting that cover two historically related concepts: the Knuth-Bendix order and the Knuth-Bendix completion procedure.
The former, besides being the first development of its kind in a proof assistant, is based on a generalized version of the Knuth-Bendix order. We compare our version to variants from the literature and show all properties required to certify termination proofs of TRSs.
The latter comprises the formalization of important facts that are related to completion, like Birkhoff\u27s theorem, the critical pair theorem, and a soundness proof of completion, showing that the strict encompassment condition is superfluous for finite runs. As a result, we are able to certify completion proofs
Certified Rule Labeling
The rule labeling heuristic aims to establish confluence of (left-)linear term rewrite systems via decreasing diagrams. We present a formalization of a confluence criterion based on the interplay of relative termination and the rule labeling in the theorem prover Isabelle. Moreover, we report on the integration of this result into the certifier CeTA, facilitating the checking of confluence certificates based on decreasing diagrams for the first time. The power of the method is illustrated by an experimental evaluation on a (standard) collection of confluence problems
AC-KBO Revisited
Equational theories that contain axioms expressing associativity and
commutativity (AC) of certain operators are ubiquitous. Theorem proving methods
in such theories rely on well-founded orders that are compatible with the AC
axioms. In this paper we consider various definitions of AC-compatible
Knuth-Bendix orders. The orders of Steinbach and of Korovin and Voronkov are
revisited. The former is enhanced to a more powerful version, and we modify the
latter to amend its lack of monotonicity on non-ground terms. We further
present new complexity results. An extension reflecting the recent proposal of
subterm coefficients in standard Knuth-Bendix orders is also given. The various
orders are compared on problems in termination and completion.Comment: 31 pages, To appear in Theory and Practice of Logic Programming
(TPLP) special issue for the 12th International Symposium on Functional and
Logic Programming (FLOPS 2014
Certified rule labeling
© Julian Nagele and Harald Zankl. The rule labeling heuristic aims to establish confluence of (left-)linear term rewrite systems via decreasing diagrams. We present a formalization of a confluence criterion based on the interplay of relative termination and the rule labeling in the theorem prover Isabelle. Moreover, we report on the integration of this result into the certifier CeTA, facilitating the checking of confluence certificates based on decreasing diagrams for the first time. The power of the method is illustrated by an experimental evaluation on a (standard) collection of confluence problems
Infinite Runs in Abstract Completion
Completion is one of the first and most studied techniques in term rewriting and fundamental to automated reasoning with equalities. In an earlier paper we presented a new and formalized correctness proof of abstract completion for finite runs. In this paper we extend our analysis and our formalization to infinite runs, resulting in a new proof that fair infinite runs produce complete presentations of the initial equations. We further consider ordered completion - an important extension of completion that aims to produce ground-complete presentations of the initial equations. Moreover, we revisit and extend results of Métivier concerning canonicity of rewrite systems. All proofs presented in the paper have been formalized in Isabelle/HOL
CERTIFYING CONFLUENCE PROOFS VIA RELATIVE TERMINATION AND RULE LABELING
The rule labeling heuristic aims to establish confluence of (left-)linear
term rewrite systems via decreasing diagrams. We present a formalization of a
confluence criterion based on the interplay of relative termination and the
rule labeling in the theorem prover Isabelle. Moreover, we report on the
integration of this result into the certifier CeTA, facilitating the checking
of confluence certificates based on decreasing diagrams. The power of the
method is illustrated by an experimental evaluation on a (standard) collection
of confluence problems
Confluence by Decreasing Diagrams -- Formalized
This paper presents a formalization of decreasing diagrams in the theorem
prover Isabelle. It discusses mechanical proofs showing that any locally
decreasing abstract rewrite system is confluent. The valley and the conversion
version of decreasing diagrams are considered.Comment: 17 pages; valley and conversion version; RTA 201
A Transfinite Knuth-Bendix Order for Lambda-Free Higher-Order Terms
International audienceWe generalize the Knuth-Bendix order (KBO) to higher-order terms without λ-abstraction. The restriction of this new order to first-order terms coincides with the traditional KBO. The order has many useful properties, including transitivity, the subterm property, compatibility with contexts (monotonicity), stability under substitution, and well-foundedness. Transfinite weights and argument coefficients can also be supported. The order appears promising as the basis of a higher-order superposition calculus
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