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20
Engineering formal metatheory
 In ACM SIGPLANSIGACT Symposium on Principles of Programming Languages
, 2008
"... Machinechecked proofs of properties of programming languages have become a critical need, both for increased confidence in large and complex designs and as a foundation for technologies such as proofcarrying code. However, constructing these proofs remains a black art, involving many choices in th ..."
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Cited by 84 (9 self)
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Machinechecked proofs of properties of programming languages have become a critical need, both for increased confidence in large and complex designs and as a foundation for technologies such as proofcarrying code. However, constructing these proofs remains a black art, involving many choices in the formulation of definitions and theorems that make a huge cumulative difference in the difficulty of carrying out large formal developments. The representation and manipulation of terms with variable binding is a key issue. We propose a novel style for formalizing metatheory, combining locally nameless representation of terms and cofinite quantification of free variable names in inductive definitions of relations on terms (typing, reduction,...). The key technical insight is that our use of cofinite quantification obviates the need for reasoning about equivariance (the fact that free names can be renamed in derivations); in particular, the structural induction principles of relations
Some lambda calculus and type theory formalized
 Journal of Automated Reasoning
, 1999
"... Abstract. We survey a substantial body of knowledge about lambda calculus and Pure Type Systems, formally developed in a constructive type theory using the LEGO proof system. On lambda calculus, we work up to an abstract, simplified, proof of standardization for beta reduction, that does not mention ..."
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Cited by 54 (7 self)
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Abstract. We survey a substantial body of knowledge about lambda calculus and Pure Type Systems, formally developed in a constructive type theory using the LEGO proof system. On lambda calculus, we work up to an abstract, simplified, proof of standardization for beta reduction, that does not mention redex positions or residuals. Then we outline the meta theory of Pure Type Systems, leading to the strengthening lemma. One novelty is our use of named variables for the formalization. Along the way we point out what we feel has been learned about general issues of formalizing mathematics, emphasizing the search for formal definitions that are convenient for formal proof and convincingly represent the intended informal concepts.
Mechanizing set theory: Cardinal arithmetic and the axiom of choice
 Journal of Automated Reasoning
, 1996
"... Abstract. Fairly deep results of ZermeloFrænkel (ZF) set theory have been mechanized using the proof assistant Isabelle. The results concern cardinal arithmetic and the Axiom of Choice (AC). A key result about cardinal multiplication is κ ⊗ κ = κ, where κ is any infinite cardinal. Proving this resu ..."
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Cited by 16 (9 self)
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Abstract. Fairly deep results of ZermeloFrænkel (ZF) set theory have been mechanized using the proof assistant Isabelle. The results concern cardinal arithmetic and the Axiom of Choice (AC). A key result about cardinal multiplication is κ ⊗ κ = κ, where κ is any infinite cardinal. Proving this result required developing theories of orders, orderisomorphisms, order types, ordinal arithmetic, cardinals, etc.; this covers most of Kunen, Set Theory, Chapter I. Furthermore, we have proved the equivalence of 7 formulations of the Wellordering Theorem and 20 formulations of AC; this covers the first two chapters of Rubin and Rubin, Equivalents of the Axiom of Choice, and involves highly technical material. The definitions used in the proofs are
Formal proofs about rewriting using ACL2
 Annals of Mathematics and Artificial Intelligence
, 2002
"... We present an application of the ACL2 theorem prover to reason about rewrite systems theory. We describe the formalization and representation aspects of our work using the firstorder, quantifierfree logic of ACL2 and we sketch some of the main points of the proof effort. First, we present a formali ..."
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Cited by 9 (1 self)
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We present an application of the ACL2 theorem prover to reason about rewrite systems theory. We describe the formalization and representation aspects of our work using the firstorder, quantifierfree logic of ACL2 and we sketch some of the main points of the proof effort. First, we present a formalization of abstract reduction systems and then we show how this abstraction can be instantiated to establish results about term rewriting. The main theorems we mechanically proved are Newman’s lemma (for abstract reductions) and Knuth–Bendix critical pair theorem (for term rewriting).
The Mechanisation of BarendregtStyle Equational Proofs (the Residual Perspective)
, 2001
"... We show how to mechanise equational proofs about higherorder languages by using the primitive proof principles of firstorder abstract syntax over onesorted variable names. We illustrate the method here by proving (in Isabelle/HOL) a technical property which makes the method widely applicable for ..."
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Cited by 8 (4 self)
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We show how to mechanise equational proofs about higherorder languages by using the primitive proof principles of firstorder abstract syntax over onesorted variable names. We illustrate the method here by proving (in Isabelle/HOL) a technical property which makes the method widely applicable for the λcalculus: the residual theory of β is renamingfree upto an initiality condition akin to the socalled Barendregt Variable Convention. We use our results to give a new diagrambased proof of the development part of the strong finite development property for the λcalculus. The proof has the same equational implications (e.g., confluence) as the proof of the full property but without the need to prove SN. We account for two other uses of the proof method, as presented elsewhere. One has been mechanised in full in Isabelle/HOL.
A proof of the churchrosser theorem for the lambda calculus in higher order logic
 TPHOLs’01: Supplemental Proceedings
, 2001
"... Abstract. This paper describes a proof of the ChurchRosser theorem within the Higher Order Logic (HOL) theorem prover. This follows the proof by Tait/MartinLöf, preserving the elegance of the classic presentation by Barendregt. We model the lambda calculus with a namecarrying syntax, as in practi ..."
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Cited by 6 (0 self)
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Abstract. This paper describes a proof of the ChurchRosser theorem within the Higher Order Logic (HOL) theorem prover. This follows the proof by Tait/MartinLöf, preserving the elegance of the classic presentation by Barendregt. We model the lambda calculus with a namecarrying syntax, as in practical languages. The proof is simplified by forming a quotient of the namecarrying syntax by the αequivalence relation, thus separating the concerns of αequivalence and βreduction. 1
Residuals in higherorder rewriting
 Proceedings of Rewriting Techniques and Applications (RTA’03
, 2003
"... Abstract. Residuals have been studied for various forms of rewriting setting. In this article we study residuals in orthogonal Pattern Rewriting Systems (PRSs). First, the rewrite relation is defined by means of a higherorder rewriting logic, and proof terms are defined that witness reductions. The ..."
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Cited by 2 (0 self)
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Abstract. Residuals have been studied for various forms of rewriting setting. In this article we study residuals in orthogonal Pattern Rewriting Systems (PRSs). First, the rewrite relation is defined by means of a higherorder rewriting logic, and proof terms are defined that witness reductions. Then, we have the formal machinery to define a residual operator for PRSs, and we will prove that an orthogonal PRS together with the residual operator mentioned above, is a residual system. As a sideeffect, all results of (abstract) residual theory are inherited by orthogonal PRSs, such as confluence, and the notion of permutation equivalence of reductions. 1
Constructive Computation Theory
 Part I.” Course Notes, DEA Informatique, Mathématiques et Applications
, 1992
"... Version 11082011 c○G. Huet 1992–2011Contents 1 λcalculus: Syntax and Computation strategies 7 1.1 Abstract syntax...................................... 7 1.2 Concrete syntax: pure λexpressions.......................... 9 ..."
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Cited by 2 (2 self)
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Version 11082011 c○G. Huet 1992–2011Contents 1 λcalculus: Syntax and Computation strategies 7 1.1 Abstract syntax...................................... 7 1.2 Concrete syntax: pure λexpressions.......................... 9
Formalising formulasastypesasobjects
 Types for Proofs and Programs
, 2000
"... Abstract. We describe a formalisation of the CurryHowardLawvere correspondence between the natural deduction system for minimal logic, the typed lambda calculus and Cartesian closed categories. We formalise the type of natural deduction proof trees as a family of sets Γ ⊢ A indexed by the current ..."
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Cited by 2 (0 self)
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Abstract. We describe a formalisation of the CurryHowardLawvere correspondence between the natural deduction system for minimal logic, the typed lambda calculus and Cartesian closed categories. We formalise the type of natural deduction proof trees as a family of sets Γ ⊢ A indexed by the current assumption list Γ and the conclusion A and organise numerous useful lemmas about proof trees categorically. We prove categorical properties about proof trees up to (syntactic) identity as well as up to βηconvertibility. We prove that our notion of proof trees is equivalent in an appropriate sense to more traditional representations of lambda terms. The formalisation is carried out in the proof assistant ALF for MartinLöf type theory. 1