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25
Equational Problems and Disunification
 Journal of Symbolic Computation
, 1989
"... Roughly speaking, an equational problem is a first order formula whose only predicate symbol is =. We propose some rules for the transformation of equational problems and study their correctness in various models. Then, we give completeness results with respect to some “simple ” problems called solv ..."
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Cited by 104 (9 self)
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Roughly speaking, an equational problem is a first order formula whose only predicate symbol is =. We propose some rules for the transformation of equational problems and study their correctness in various models. Then, we give completeness results with respect to some “simple ” problems called solved forms. Such completeness results still hold when adding some control which moreover ensures termination. The termination proofs are given for a “weak ” control and thus hold for the (large) class of algorithms obtained by restricting the scope of the rules. Finally, it must be noted that a byproduct of our method is a decision procedure for the validity in the Herbrand Universe of any
Theorem Proving Modulo
 Journal of Automated Reasoning
"... Abstract. Deduction modulo is a way to remove computational arguments from proofs by reasoning modulo a congruence on propositions. Such a technique, issued from automated theorem proving, is of much wider interest because it permits to separate computations and deductions in a clean way. The first ..."
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Cited by 76 (14 self)
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Abstract. Deduction modulo is a way to remove computational arguments from proofs by reasoning modulo a congruence on propositions. Such a technique, issued from automated theorem proving, is of much wider interest because it permits to separate computations and deductions in a clean way. The first contribution of this paper is to define a sequent calculus modulo that gives a proof theoretic account of the combination of computations and deductions. The congruence on propositions is handled via rewrite rules and equational axioms. Rewrite rules apply to terms and also directly to atomic propositions. The second contribution is to give a complete proof search method, called Extended Narrowing and Resolution (ENAR), for theorem proving modulo such congruences. The completeness of this method is proved with respect to provability in sequent calculus modulo. An important application is that higherorder logic can be presented as a theory modulo. Applying the Extended Narrowing and Resolution method to this presentation of higherorder logic subsumes full higherorder resolution.
Completeness Results for Basic Narrowing
, 1994
"... In this paper we analyze completeness results for basic narrowing. We show that basic narrowing is not complete with respect to normalizable solutions for equational theories defined by confluent term rewriting systems, contrary to what has been conjectured. By imposing syntactic restrictions on the ..."
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Cited by 44 (2 self)
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In this paper we analyze completeness results for basic narrowing. We show that basic narrowing is not complete with respect to normalizable solutions for equational theories defined by confluent term rewriting systems, contrary to what has been conjectured. By imposing syntactic restrictions on the rewrite rules we recover completeness. We refute a result of Holldobler which states the completeness of basic conditional narrowing for complete (i.e. confluent and terminating) conditional term rewriting systems without extra variables in the conditions of the rewrite rules. In the last part of the paper we extend the completeness result of Giovannetti and Moiso for levelconfluent and terminating conditional systems with extra variables in the conditions to systems that may also have extra variables in the righthand sides of the rules. 1985 Mathematics Subject Classification: 68Q50 1987 CR Categories: F.4.1, F.4.2 Key Words and Phrases: narrowing, basic narrowing, conditional narrowin...
The finite variant property: How to get rid of some algebraic properties
 In Proceedings of RTA’05, LNCS 3467
, 2005
"... Abstract. We consider the following problem: Given a term t, a rewrite system R, a finite set of equations E ′ such that R is E ′convergent, compute finitely many instances of t: t1,..., tn such that, for every substitution σ, there is an index i and a substitution θ such that tσ ↓ =E ′ tiθ (wher ..."
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Cited by 39 (9 self)
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Abstract. We consider the following problem: Given a term t, a rewrite system R, a finite set of equations E ′ such that R is E ′convergent, compute finitely many instances of t: t1,..., tn such that, for every substitution σ, there is an index i and a substitution θ such that tσ ↓ =E ′ tiθ (where tσ ↓ is the normal form of tσ w.r.t. →E ′ \R). The goal of this paper is to give equivalent (resp. sufficient) conditions for the finite variant property and to systematically investigate this property for equational theories, which are relevant to security protocols verification. For instance, we prove that the finite variant property holds for Abelian Groups, and a theory of modular exponentiation and does not hold for the theory ACUNh (Associativity, Commutativity, Unit, Nilpotence, homomorphism).
Extension of ML Type System with a Sorted Equational Theory on Types
, 1992
"... We extend the ML language by allowing a sorted regular equational theory on types for which unification is decidable and unitary. We prove that the extension keeps principal typings and subject reduction. A new set of typing rules is proposed so that type generalization is simpler and more efficient ..."
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Cited by 34 (11 self)
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We extend the ML language by allowing a sorted regular equational theory on types for which unification is decidable and unitary. We prove that the extension keeps principal typings and subject reduction. A new set of typing rules is proposed so that type generalization is simpler and more efficient. We consider typing problems as general unification problems, which we solve with a formalism of unificands. Unificands naturally deal with sharing between types and lead to a more efficient type inference algorithm. The use of unificands also simplifies the proof of correctness of the algorithm by splitting it into more elementary steps. Extension du syst`eme de type de ML par une th'eorie 'equationnelle avec sortes sur les types R'esum'e Le typage du langage ML est 'etendu en consid'erant les types modulo une th'eorie 'equationnelle r'eguli`ere avec sortes pour laquelle l'unification est d'ecidable. Cette extension conserve la propri'et'e d'avoir un type principal ainsi que la conservatio...
A New Method for Undecidability Proofs of First Order Theories
 Journal of Symbolic Computation
, 1992
"... this paper is to define a framework for such reduction proofs. The method proposed is illustrated by proving the undecidability of the theory of a term algebra modulo the axioms of associativity and commutativity and of the theory of a partial lexicographic path ordering. 1. Introduction ..."
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Cited by 30 (7 self)
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this paper is to define a framework for such reduction proofs. The method proposed is illustrated by proving the undecidability of the theory of a term algebra modulo the axioms of associativity and commutativity and of the theory of a partial lexicographic path ordering. 1. Introduction
Combining Symbolic Constraint Solvers on Algebraic Domains
 Journal of Symbolic Computation
, 1994
"... ion An atomic constraint p ? (t 1 ; : : : ; t m ) is decomposed into a conjunction of pure atomic constraints by introducing new equations of the form (x = ? t), where t is an alien subterm in the constraint and x is a variable that does not appear in p ? (t 1 ; : : : ; t m ). This is formalized tha ..."
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Cited by 28 (7 self)
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ion An atomic constraint p ? (t 1 ; : : : ; t m ) is decomposed into a conjunction of pure atomic constraints by introducing new equations of the form (x = ? t), where t is an alien subterm in the constraint and x is a variable that does not appear in p ? (t 1 ; : : : ; t m ). This is formalized thanks to the notion of abstraction. Definition 4.2. Let T be a set of terms such that 8t 2 T ; 8u 2 X [ SC; t 6= E1[E2 u: A variable abstraction of the set of terms T is a surjective mapping \Pi from T to a set of variables included in X such that 8s; t 2 T ; \Pi(s) = \Pi(t) if and only if s =E1[E2 t: \Pi \Gamma1 denotes any substitution (with possibly infinite domain) such that \Pi(\Pi \Gamma1 (x)) = x for any variable x in the range of \Pi. It is important to note that building a variable abstraction relies on the decidability of E 1 [ E 2 equality in order to abstract equal alien subterms by the same variable. Let T = fu #R j u 2 T (F [ X ) and u #R2 T (F [ X )n(X [ SC)g...
Combination Techniques for NonDisjoint Equational Theories
 Proceedings 12th International Conference on Automated Deduction
, 1994
"... ion variables which are variables coming from an abstraction, either during preprocessing or during the algorithm itself. 3. Introduced variables which are variables introduced by the unification algorithms for each theory. We make the very natural assumption that the unification algorithm for each ..."
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Cited by 24 (4 self)
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ion variables which are variables coming from an abstraction, either during preprocessing or during the algorithm itself. 3. Introduced variables which are variables introduced by the unification algorithms for each theory. We make the very natural assumption that the unification algorithm for each theory may recognize initial, abstraction and introduced variables and never assigns an introduced variable to a nonintroduced one or an abstraction variable to an initial one. With this assumption, our combination algorithm will always make an introduced variable appear in at most one \Gamma i . We may thus also suppose that the domain of each solution does not contain an introduced variable. This does not compromise the soundness of our algorithm. The combination algorithm is described by the two rules given in figure 2. In the rule UnifSolve i , ae SF is obtained by abstracting aliens in the range of ae by fresh variables. ae F i is the substitution such that xae = xae SF ae F i for al...
Birewriting, a Term Rewriting Technique for Monotonic Order Relations
 Rewriting Techniques and Applications, LNCS 690
, 1993
"... We propose an extension of rewriting techniques to derive inclusion relations $a \subseteq b$ between terms built from monotonic operators. Instead of using only a rewriting relation $\REa$ and rewriting $a$ to $b$, we use another rewriting relation $\REb$ as well and seek a common expression $c$ su ..."
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Cited by 22 (6 self)
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We propose an extension of rewriting techniques to derive inclusion relations $a \subseteq b$ between terms built from monotonic operators. Instead of using only a rewriting relation $\REa$ and rewriting $a$ to $b$, we use another rewriting relation $\REb$ as well and seek a common expression $c$ such that $a \REa^* c$ and $b \REb^* c$. Each component of the birewriting system $\pair{\REa}{\REb}$ is allowed to be a subset of the corresponding inclusion $\subseteq$ or $\superseteq$. In order to assure the decidability and completeness of the proof procedure we study the commutativity of $\REa$ and $\REb$. We also extend the existing techniques of rewriting modulo equalities to birewriting modulo a set of inclusions. We present the canonical birewriting system corresponding to the theory of nondistributive lattices.
Syntactic Theories and the Algebra of Record Terms
, 1993
"... Recently, many type systems for records have been proposed. For most of them, the types cannot be described as the terms of an algebra. In this case, type checking, or type inference in the case of first order type systems, cannot be derived from existing algorithms. We define record terms as the te ..."
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Cited by 21 (5 self)
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Recently, many type systems for records have been proposed. For most of them, the types cannot be described as the terms of an algebra. In this case, type checking, or type inference in the case of first order type systems, cannot be derived from existing algorithms. We define record terms as the terms of an equational algebra. We prove decidability of the unification problem for records terms by showing that its equational theory is syntactic. We derive a complete algorithm and prove its termination. We define a notion of canonical terms and approximations of record terms by canonical terms, and show that approximations commute with unification. We also study generic record terms, which extend record terms to model a form of sharing between terms. We prove that the equational theory of generic record terms and that the corresponding unification algorithm always terminates.