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21
Unification and AntiUnification in the Calculus of Constructions
 In Sixth Annual IEEE Symposium on Logic in Computer Science
, 1991
"... We present algorithms for unification and antiunification in the Calculus of Constructions, where occurrences of free variables (the variables subject to instantiation) are restricted to higherorder patterns, a notion investigated for the simplytyped calculus by Miller. Most general unifiers and ..."
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Cited by 61 (15 self)
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We present algorithms for unification and antiunification in the Calculus of Constructions, where occurrences of free variables (the variables subject to instantiation) are restricted to higherorder patterns, a notion investigated for the simplytyped calculus by Miller. Most general unifiers and least common antiinstances are shown to exist and are unique up to a simple equivalence. The unification algorithm is used for logic program execution and type and term reconstruction in the current implementation of Elf and has shown itself to be practical. The main application of the antiunification algorithm we have in mind is that of proof generalization. 1 Introduction Higherorder logic with an embedded simplytyped  calculus has been used as the basis for a number of theorem provers (for example [1, 19]) and the programming language Prolog [16]. Central to these systems is an implementation of Huet's preunification algorithm for the simplytyped calculus [12] which has shown it...
A Generic Approach to Building User Interfaces for Theorem Provers
 JOURNAL OF SYMBOLIC COMPUTATION
, 1995
"... In this paper, we present the results of an ongoing effort in building user interfaces for proof systems. Our approach is generic: we are not constructiong a user interface for a particular proof system, rather we have developed techniques and tools... ..."
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Cited by 28 (8 self)
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In this paper, we present the results of an ongoing effort in building user interfaces for proof systems. Our approach is generic: we are not constructiong a user interface for a particular proof system, rather we have developed techniques and tools...
An algorithm for deciding BAPA: Boolean Algebra with Presburger Arithmetic
 In 20th International Conference on Automated Deduction, CADE20
, 2005
"... Abstract. We describe an algorithm for deciding the firstorder multisorted theory BAPA, which combines 1) Boolean algebras of sets of uninterpreted elements (BA) and 2) Presburger arithmetic operations (PA). BAPA can express the relationship between integer variables and cardinalities of a priory u ..."
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Cited by 26 (13 self)
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Abstract. We describe an algorithm for deciding the firstorder multisorted theory BAPA, which combines 1) Boolean algebras of sets of uninterpreted elements (BA) and 2) Presburger arithmetic operations (PA). BAPA can express the relationship between integer variables and cardinalities of a priory unbounded finite sets, and supports arbitrary quantification over sets and integers. Our motivation for BAPA is deciding verification conditions that arise in the static analysis of data structure consistency properties. Data structures often use an integer variable to keep track of the number of elements they store; an invariant of such a data structure is that the value of the integer variable is equal to the number of elements stored in the data structure. When the data structure content is represented by a set, the resulting constraints can be captured in BAPA. BAPA formulas with quantifier alternations arise when verifying programs with annotations containing quantifiers, or when proving simulation relation conditions for refinement and equivalence of program fragments. Furthermore, BAPA constraints can be used for proving the termination of programs that manipulate data structures, and have applications in constraint databases. We give a formal description of a decision procedure for BAPA, which implies the decidability of BAPA. We analyze our algorithm and obtain an elementary upper bound on the running time, thereby giving the first complexity bound for BAPA. Because it works by a reduction to PA, our algorithm yields the decidability of a combination of sets of uninterpreted elements with any decidable extension of PA. Our algorithm can also be used to yield an optimal decision procedure for BA through a reduction to PA with bounded quantifiers. We have implemented our algorithm and used it to discharge verification conditions in the Jahob system for data structure consistency checking of Java programs; our experience with the algorithm is promising. 1
Decidable higherorder unification problems
 AUTOMATED DEDUCTION  CADE12. SPRINGER LNAI 814
, 1994
"... Secondorder unification is undecidable in general. Miller showed that unification of socalled higherorder patterns is decidable and unitary. Weshow that the unification of a linear higherorder pattern s with an arbitrary secondorder term that shares no variables with s is decidable and finitar ..."
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Cited by 17 (4 self)
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Secondorder unification is undecidable in general. Miller showed that unification of socalled higherorder patterns is decidable and unitary. Weshow that the unification of a linear higherorder pattern s with an arbitrary secondorder term that shares no variables with s is decidable and finitary. A few extensions of this unification problem are still decidable: unifying two secondorder terms, where one term is linear, is undecidable if the terms contain bound variables but decidable if they don't.
Presenting intuitive deductions via symmetric simplification
 In CADE10: Proceedings of the tenth international conference on Automated deduction
, 1990
"... In automated deduction systems that are intended for human use, the presentation of a proof is no less important than its discovery. For most of today’s automated theorem proving systems, this requires a nontrivial translation procedure to extract humanoriented deductions from machineoriented pro ..."
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Cited by 15 (4 self)
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In automated deduction systems that are intended for human use, the presentation of a proof is no less important than its discovery. For most of today’s automated theorem proving systems, this requires a nontrivial translation procedure to extract humanoriented deductions from machineoriented proofs. Previously known translation procedures, though complete, tend to produce unintuitive deductions. One of the major flaws in such procedures is that too often the rule of indirect proof is used where the introduction of a lemma would result in a shorter and more intuitive proof. We present an algorithm, symmetric simplification, for discovering useful lemmas in deductions of theorems in first and higherorder logic. This algorithm, which has been implemented in the TPS system, has the feature that resulting deductions may no longer have the weak subformula property. It is currently limited, however, in that it only generates lemmas of the form C ∨ ¬C ′ , where C and C ′ have the same negation normal form. 1
How to Prove Higher Order Theorems in First Order Logic
 PROCEEDINGS OF THE 12TH IJCAI
, 1991
"... In this paper we are interested in using a first order theorem prover to prove theorems that are formulated in some higher order logic. To this end we present translations of higher order logics into first order logic with flat sorts and equality and give a sufficient criterion for the soundness of ..."
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Cited by 12 (5 self)
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In this paper we are interested in using a first order theorem prover to prove theorems that are formulated in some higher order logic. To this end we present translations of higher order logics into first order logic with flat sorts and equality and give a sufficient criterion for the soundness of these translations. In addition translations are introduced that are sound and complete with respect to L. Henkin's general model semantics. Our higher order logics are based on a restricted type structure in the sense of A. Church, they have typed function symbols and predicate symbols, but no sorts.
Using Decision Procedures With a HigherOrder Logic
 In Theorem Proving in Higher Order Logics: 14th International Conference, TPHOLs 2001
, 2001
"... In automated reasoning, there is a perceived tradeo between expressiveness and automation. Higherorder logic is typically viewed as expressive but resistant to automation, in contrast with rstorder logic and its fragments. We argue that higherorder logic and its variants actually achieve a happy ..."
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Cited by 8 (2 self)
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In automated reasoning, there is a perceived tradeo between expressiveness and automation. Higherorder logic is typically viewed as expressive but resistant to automation, in contrast with rstorder logic and its fragments. We argue that higherorder logic and its variants actually achieve a happy medium between expressiveness and automation, particularly when used as a frontend to a wide range of decision procedures and deductive procedures. We illustrate the discussion with examples from PVS, but some of the observations apply to other variants of higherorder logic as well.
A Calculus and a System Architecture for Extensional HigherOrder Resolution
, 1997
"... The first part of this paper introduces an extension for a variant of Huet's higherorder resolution calculus [Hue72, Hue73] based upon classical type theory (Church's typed calculus [Chu40]) in order to obtain a calculus which is complete with respect to Henkin models [Hen50]. The new rules connec ..."
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Cited by 8 (5 self)
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The first part of this paper introduces an extension for a variant of Huet's higherorder resolution calculus [Hue72, Hue73] based upon classical type theory (Church's typed calculus [Chu40]) in order to obtain a calculus which is complete with respect to Henkin models [Hen50]. The new rules connect higherorder preunification with the general refutation process in an appropriate way to establish full extensionality for the whole system. The general idea of the calculus is discussed on different examples. The second part introduces the Leo system which implements the discussed extensional higherorder resolution calculus. This part mainly focus on the embedding of the new extensionality rules into the refutation process and the treatment of higherorder unification. 1 Introduction Many mathematical problems can be expressed shortly and elegantly in higher order logic whereas they often lead to unnatural and inflated formulations in firstorder logic, e.g., when coding them into axio...
On the Translation of HigherOrder Problems into FirstOrder Logic
 Proceedings of ECAI94
, 1994
"... . In most cases higherorder logic is based on the  calculus in order to avoid the infinite set of socalled comprehension axioms. However, there is a price to be paid, namely an undecidable unification algorithm. If we do not use the calculus, but translate higherorder expressions into firstor ..."
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Cited by 6 (4 self)
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. In most cases higherorder logic is based on the  calculus in order to avoid the infinite set of socalled comprehension axioms. However, there is a price to be paid, namely an undecidable unification algorithm. If we do not use the calculus, but translate higherorder expressions into firstorder expressions by standard translation techniques, we have to translate the infinite set of comprehension axioms, too. Of course, in general this is not practicable. Therefore such an approach requires some restrictions such as the choice of the necessary axioms by a human user or the restriction to certain problem classes. This paper will show how the infinite class of comprehension axioms can be represented by a finite subclass, so that an automatic translation of finite higherorder problems into finite firstorder problems is possible. This translation is sound and complete with respect to a Henkinstyle general model semantics. 1 Introduction Firstorder logic is a powerful tool for ...