We describe the superposition-based theorem prover E. E is a sound and complete...

Theorem provers based on model elimination have exhibited extremely high inference rates but have lacked a redundancy control mechanism such as subsumption. In this paper we report on work done to modify a model elimination theorem prover using two techniques, caching and lemmaizing, that have reduced by more than an order of magnitude the time required to find proofs of several problems and that have enabled the prover to prove theorems previously unobtainable by top-down model elimination theorem provers.

1.1 Quantification and the subformula property.................. 3 1.2 Ground forward sequent calculus......................... 5 1.3 Lifting to free variables............................... 10

First-order languages based on rewrite rules share many features with functional languages. But one difference is that matching and rewriting can be made much more expressive and powerful by incorporating some built-in equational theories. To provide reasonable programming environments, compilation techniques for such languages based on rewriting have to be designed. This is the topic addressed in this paper. The proposed techniques are independent from the rewriting language and may be useful to build a compiler for any system using rewriting modulo associative and commutative (AC) theories. An algorithm for many-to-one AC matching is presented, that works efficiently for a restricted class of patterns. Other patterns are transformed to fit into this class. A refined data structure, namely compact bipartite graph, allows encoding all matching problems relative to a set of rewrite rules. A few optimisations concerning the construction of the substitution and of the reduced term are described. We also address the problem of non-determinism related to AC rewriting and show how to handle it through the concept of strategies. We explain how an analysis of the determinism can be performed at compile time and we illustrate the benefits of this analysis for the performance of the compiled evaluation process. Then we briefly introduce the ELAN system and its compiler, in order to give some experimental results and comparisons with other languages or rewrite engines.

This article describes the design, implementation, and experimental evaluation of data structures and algorithms for high-performance table access. Our approach uses tries as the basis for tables. Tries, a variant of discrimination nets, provide complete discrimination for terms, and permit a lookup and possible insertion to be performed in a single pass through a term. In addition, a novel technique of substitution factoring is proposed. When substitution factoring is used, the access cost for answers is proportional to the size of the answer substitution, rather than to the size of the answer itself. Answer tries can be implemented both as interpreted structures and as compiled WAM-like code. When they are compiled, the speed of computing substitutions through answer tries is competitive with the speed of unit facts compiled or asserted as WAM code. Because answer tries can also be created an order of magnitude more quickly than asserted code, they form a promising alternative for representing certain types of dynamic code, even in Prolog systems without tabling. / Address correspondence to I.V. Ramakrishnan, D.S. Warren, Dept. of Computer Science, State University of New York at Stony Brook, Stony Brook, NY 11794-4400, U.S.A., email: fram,warreng@cs.sunysb.edu; P. Rao, Bellcore, 445 South Street, Morristown, NJ 07960-6438, U.S.A., e-mail: prasadr@bellcore.com; K. Sagonas, Dept. of Computer Science, Katholieke Universiteit Leuven, Celestijnenlaan 200A, B-3001, Heverlee, Belgium, email:

The performance of a theorem prover crucially depends on the speed of the basic retrieval operations, such as finding terms that are unifiable with (instances of, or more general than) a given query term. In this paper a new indexing method is presented, which outperforms traditional methods such as path indexing, discrimination tree indexing and abstraction trees. Additionally, the new index not only supports term indexing but also provides maintenance and efficient retrieval of substitutions. As confirmed in multiple experiments, substitution trees combine maximal search speed and minimal memory requirements.

Abstract. LEO-II is a standalone, resolution-based higher-order theorem prover designed for effective cooperation with specialist provers for natural fragments of higher-order logic. At present LEO-II can cooperate with the first-order automated theorem provers E, SPASS, and Vampire. The improved performance of LEO-II, especially in comparison to its predecessor LEO, is due to several novel features including the exploitation of term sharing and term indexing techniques, support for primitive equality reasoning, and improved heuristics at the calculus level. LEO-II is implemented in Objective Caml and its problem representation language is the new TPTP THF language. 1

: In this report we give an overview of the development of our new Waldmeister prover for equational theories. We elaborate a systematic stepwise design process, starting with the inference system for unfailing Knuth--Bendix completion and ending up with an implementation which avoids the main diseases today's provers suffer from: overindulgence in time and space. Our design process is based on a logical three--level system model consisting of basic operations for inference step execution, aggregated inference machine, and overall control strategy. Careful analysis of the inference system for unfailing completion has revealed the crucial points responsible for time and space consumption. For the low level of our model, we introduce specialized data structures and algorithms speeding up the running system and cutting it down in size --- both by one order of magnitude compared with standard techniques. Flexible control of the mid--level aggregation inside the resulting prover is made po...

Devices]: Models of Computation---automata; F.2.2 [Analysis of Algorithms and Problem Complexity]: Nonnumerical Algorithms and Problems---pattern matching General Terms: Algorithms, Languages, Theory Additional Key Words and Phrases: Indexing, logic programming, trie minimization, unification 1. INTRODUCTION In logic programming languages, such as Prolog, a predicate is defined by a sequence of Horn clauses. A clause becomes applicable for resolution if its head unifies with a selected goal; and each applicable clause is invoked in textual order. Unification of a clause head with a goal involves two basic types of operations: elementary match operations and substitution operations for variables in the two A preliminary version of this article was presented at POPL '95. This work was supported in part by NSF grants CCR-9102159, CCR-9102989, CCR-9404921, CDA-9303181, CDA-9504275, INT-9314412, and ONR grant 400X116YIP01. Authors' addresses: S. Dawson, Computer Science Laboratory, SRI In...

Gaining efficiency in completion-based theorem proving requires improvements on three levels: fast inference step execution, careful aggregation into an inference machine, and sophisticated control strategies, all that combined with space saving representation of derived facts.