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Focusing the inverse method for linear logic
 Proceedings of CSL 2005
, 2005
"... 1.1 Quantification and the subformula property.................. 3 1.2 Ground forward sequent calculus......................... 5 1.3 Lifting to free variables............................... 10 ..."
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1.1 Quantification and the subformula property.................. 3 1.2 Ground forward sequent calculus......................... 5 1.3 Lifting to free variables............................... 10
Semantic Types: A Fresh Look at the Ideal Model for Types
, 2004
"... We present a generalization of the ideal model for recursive polymorphic types. Types are defined as sets of terms instead of sets of elements of a semantic domain. Our proof of the existence of types (computed by fixpoint of a typing operator) does not rely on metric properties, but on the fact tha ..."
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Cited by 24 (2 self)
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We present a generalization of the ideal model for recursive polymorphic types. Types are defined as sets of terms instead of sets of elements of a semantic domain. Our proof of the existence of types (computed by fixpoint of a typing operator) does not rely on metric properties, but on the fact that the identity is the limit of a sequence of projection terms. This establishes a connection with the work of Pitts on relational properties of domains. This also suggests that ideals are better understood as closed sets of terms defined by orthogonality with respect to a set of contexts.
Focusing on binding and computation
 In 23rd Symposium on Logic in Computer Science
, 2008
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On the unity of duality
 Special issue on “Classical Logic and Computation
, 2008
"... Most type systems are agnostic regarding the evaluation strategy for the underlying languages, with the value restriction for ML which is absent in Haskell as a notable exception. As type systems become more precise, however, detailed properties of the operational semantics may become visible becaus ..."
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Most type systems are agnostic regarding the evaluation strategy for the underlying languages, with the value restriction for ML which is absent in Haskell as a notable exception. As type systems become more precise, however, detailed properties of the operational semantics may become visible because properties captured by the types may be sound under one strategy but not the other. For example, intersection types distinguish between callbyname and callbyvalue functions, because the subtyping law (A → B) ∩ (A → C) ≤ A → (B ∩ C) is unsound for the latter in the presence of effects. In this paper we develop a prooftheoretic framework for analyzing the interaction of types with evaluation order, based on the notion of polarity. Polarity was discovered through linear logic, but we propose a fresh origin in Dummett’s program of justifying the logical laws through alternative verificationist or pragmatist “meaningtheories”, which include a bias towards either introduction or elimination rules. We revisit Dummett’s analysis using the tools of MartinLöf’s judgmental method, and then show how to extend it to a unified polarized logic, with Girard’s “shift ” connectives acting as intermediaries. This logic safely combines intuitionistic and dual intuitionistic reasoning principles, while simultaneously admitting a focusing interpretation for the classical sequent calculus. Then, by applying the CurryHoward isomorphism to polarized logic, we obtain a single programming language in which evaluation order is reflected at the level of types. Different logical notions correspond directly to natural programming constructs, such as patternmatching, explicit substitutions, values and callbyvalue continuations. We give examples demonstrating the expressiveness of the language and type system, and prove a basic but modular type safety result. We conclude with a brief discussion of extensions to the language with additional effects and types, and sketch the sort of explanation this can provide for operationallysensitive typing phenomena. 1
2010): An exact correspondence between a typed picalculus and polarised proofnets
 Theor. Comput. Sci
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Dependently Typed Programming with DomainSpecific Logics
 SUBMITTED TO POPL ’09
, 2008
"... We define a dependent programming language in which programmers can define and compute with domainspecific logics, such as an accesscontrol logic that statically prevents unauthorized access to controlled resources. Our language permits programmers to define logics using the LF logical framework, ..."
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We define a dependent programming language in which programmers can define and compute with domainspecific logics, such as an accesscontrol logic that statically prevents unauthorized access to controlled resources. Our language permits programmers to define logics using the LF logical framework, whose notion of binding and scope facilitates the representation of the consequence relation of a logic, and to compute with logics by writing functional programs over LF terms. These functional programs can be used to compute values at runtime, and also to compute types at compiletime. In previous work, we studied a simplytyped framework for representing and computing with variable binding [LICS 2008]. In this paper, we generalize our previous type theory to account for dependently typed inference rules, which are necessary to adequately represent domainspecific logics, and we present examples of using our type theory for certified software and mechanized metatheory.
Focalisation and classical realisability
 In Computer Science Logic ’09, LNCS
, 2009
"... Abstract We develop a polarised variant of Curien and Herbelin’s λ̄µµ ̃ calculus suitable for sequent calculi that admit a focalising cut elimination (i.e. whose proofs are focalised when cutfree), such as Girard’s classical logic LC or linear logic. This gives a setting in which Krivine’s classic ..."
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Abstract We develop a polarised variant of Curien and Herbelin’s λ̄µµ ̃ calculus suitable for sequent calculi that admit a focalising cut elimination (i.e. whose proofs are focalised when cutfree), such as Girard’s classical logic LC or linear logic. This gives a setting in which Krivine’s classical realisability extends naturally (in particular to callbyvalue), with a presentation in terms of orthogonality. We give examples of applications to the theory of programming languages. In this version extended with appendices, we in particular give the twosided formulation of classical logic with the involutive classical negation. We also show that there is, in classical realisability, a notion of internal complete
A system of interaction and structure V: The exponentials and splitting
, 2009
"... System NEL is the mixed commutative/noncommutative linear logic BV augmented with linear logic’s exponentials, or, equivalently, it is MELL augmented with the noncommutative selfdual connective seq. System NEL is Turingcomplete, it is able to directly express process algebra sequential compositio ..."
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System NEL is the mixed commutative/noncommutative linear logic BV augmented with linear logic’s exponentials, or, equivalently, it is MELL augmented with the noncommutative selfdual connective seq. System NEL is Turingcomplete, it is able to directly express process algebra sequential composition and it faithfully models causal quantum evolution. In this paper, we show cut elimination for NEL, based on a property that we call splitting. NEL is presented in the calculus of structures, which is a deepinference formalism, because no Gentzen formalism can express it analytically. The splitting theorem shows how and to what extent we can recover a sequentlike structure in NEL proofs. Together with the decomposition theorem, proved in the previous paper of the series, this immediately leads to a cutelimination theorem for NEL. 1
Positively Dependent Types
 SUBMITTED TO PLPV ’09
, 2008
"... This paper is part of a line of work on using the logical techniques of polarity and focusing to design a dependent programming language, with particular emphasis on programming with deductive systems such as programming languages and proof theories. Polarity emphasizes the distinction between posit ..."
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Cited by 4 (0 self)
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This paper is part of a line of work on using the logical techniques of polarity and focusing to design a dependent programming language, with particular emphasis on programming with deductive systems such as programming languages and proof theories. Polarity emphasizes the distinction between positive types, which classify data, and negative types, which classify computation. In previous work, we showed how to use Zeilberger’s higherorder formulation of focusing to integrate a positive function space for representing variable binding, an essential tool for specifying logical systems, with a standard negative computational function space. However, our previous work considers only a simplytyped language. The central technical contribution of the present paper is to extend higherorder focusing with a form of dependency that we call positively dependent types: We allow dependency on positive data, but not negative computation, and we present the syntax of dependent pair and function types using an iterated inductive definition, mapping positive data to types, which gives an account of typelevel computation. We construct our language inside the dependently typed programming language Agda 2, making essential use of coinductive types and inductionrecursion.
Polarity and the Logic of Delimited Continuations
"... Abstract—Polarized logic is the logic of values and continuations, and their interaction through continuationpassing style. The main limitations of this logic are the limitations of CPS: that continuations cannot be composed, and that programs are fully sequentialized. Delimited control operators w ..."
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Abstract—Polarized logic is the logic of values and continuations, and their interaction through continuationpassing style. The main limitations of this logic are the limitations of CPS: that continuations cannot be composed, and that programs are fully sequentialized. Delimited control operators were invented in response to the limitations of classical continuationpassing. That suggests the question: what is the logic of delimited continuations? We offer a simple account of delimited control, through a natural generalization of the classical notion of polarity. This amounts to breaking the perfect symmetry between positive and negative polarity in the following way: answer types are positive. Despite this asymmetry, we retain all of the classical polarized connectives, and can explain “intuitionistic polarity ” (e.g., in systems like CBPV) as a restriction on the use of connectives, i.e., as a logical fragment. Our analysis complements and generalizes existing accounts of delimited control operators, while giving us a rich logical language through which to understand the interaction of control with monadic effects. I.