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Constructions, Inductive Types and Strong Normalization
, 1993
"... This thesis contains an investigation of Coquand's Calculus of Constructions, a basic impredicative Type Theory. We review syntactic properties of the calculus, in particular decidability of equality and typechecking, based on the equalityasjudgement presentation. We present a settheoretic notio ..."
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Cited by 31 (2 self)
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This thesis contains an investigation of Coquand's Calculus of Constructions, a basic impredicative Type Theory. We review syntactic properties of the calculus, in particular decidability of equality and typechecking, based on the equalityasjudgement presentation. We present a settheoretic notion of model, CCstructures, and use this to give a new strong normalization proof based on a modification of the realizability interpretation. An extension of the core calculus by inductive types is investigated and we show, using the example of infinite trees, how the realizability semantics and the strong normalization argument can be extended to nonalgebraic inductive types. We emphasize that our interpretation is sound for large eliminations, e.g. allows the definition of sets by recursion. Finally we apply the extended calculus to a nontrivial problem: the formalization of the strong normalization argument for Girard's System F. This formal proof has been developed and checked using the...
A Formalization of the Strong Normalization Proof for System F in LEGO
, 1993
"... We describe a complete formalization of a strong normalization proof for the Curry style presentation of System F in LEGO. The underlying type theory is the Calculus of Constructions enriched by inductive types. The proof follows Girard et al [GLT89], i.e. we use the notion of candidates of reducibi ..."
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Cited by 7 (0 self)
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We describe a complete formalization of a strong normalization proof for the Curry style presentation of System F in LEGO. The underlying type theory is the Calculus of Constructions enriched by inductive types. The proof follows Girard et al [GLT89], i.e. we use the notion of candidates of reducibility, but we make essential use of general inductive types to simplify the presentation. We discuss extensions and variations of the proof: the extraction of a normalization function, the use of saturated sets instead of candidates, and the extension to a Church Style presentation. We conclude with some general observations about Computer Aided Formal Reasoning.
Inheritance of Proofs
, 1996
"... The CurryHoward isomorphism, a fundamental property shared by many type theories, establishes a direct correspondence between programs and proofs. This suggests that the same structuring principles that ease programming be used to simplify proving as well. To exploit objectoriented structuring me ..."
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Cited by 4 (0 self)
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The CurryHoward isomorphism, a fundamental property shared by many type theories, establishes a direct correspondence between programs and proofs. This suggests that the same structuring principles that ease programming be used to simplify proving as well. To exploit objectoriented structuring mechanisms for verification, we extend the objectmodel of Pierce and Turner, based on the higher order typed calculus F ! , with a proof component. By enriching the (functional) signature of objects with a specification, the methods and their correctness proofs are packed together in the objects. The uniform treatment of methods and proofs gives rise in a natural way to objectoriented proving principles  including inheritance of proofs, late binding of proofs, and encapsulation of proofs  as analogues to objectoriented programming principles. We have used Lego, a typetheoretic proof checker, to explore the feasibility of this approach. In particular, we have verified a small hier...
A TypeTheoretic Analysis of Modular Specifications
, 1996
"... We study the problem of representing a modular specification language in a typetheory based theorem prover. Our goals are: to provide mechanical support for reasoning about specifications and about the specification language itself; to clarify the semantics of the specification language by formalis ..."
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Cited by 2 (1 self)
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We study the problem of representing a modular specification language in a typetheory based theorem prover. Our goals are: to provide mechanical support for reasoning about specifications and about the specification language itself; to clarify the semantics of the specification language by formalising them fully; to augment the specification language with a programming language in a setting where they are both part of the same formal environment, allowing us to define a formal implementation relationship between the two. Previous work on similar issues has given rise to a dichotomy between “shallow ” and “deep ” embedding styles when representing one language within another. We show that the expressiveness of type theory, and the high degree of reflection that it permits, allow us to develop embedding techniques which lie between the “shallow ” and “deep ” extremes. We consider various possible embedding strategies and then choose one of them to explore more fully. As our object of study we choose a fragment of the Z specification language, which we encode in the type theory UTT, as implemented in the LEGO proofchecker. We use the encoding to study some of the operations on schemas provided by Z. One of our main concerns is whether it is possible to reason about Z specifications at the level of these operations. We prove some theorems about Z showing that, within certain constraints, this kind of reasoning is indeed possible. We then show how these metatheorems can be used to carry out formal reasoning about Z specifications. For this we make use of an example taken from the Z Reference Manual (ZRM). Finally, we exploit the fact that type theory provides a programming language as well as a logic to define a notion of implementation for Z specifications. We illustrate this by encoding some example programs taken from the ZRM. ii Declaration I declare that this thesis was composed by myself, and that the work contained in it is my own except where otherwise stated. Some of this work has been published previously [Mah94]. iii