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Comparing and Implementing Calculi of Explicit Substitutions with Eta Reduction
 Annals of Pure and Applied Logic
, 2005
"... The past decade has seen an explosion of work on calculi of explicit substitutions. Numerous work has illustrated the usefulness of these calculi for practical notions like the implementation of typed functional programming languages and higher order proof assistants. It has also been shown that e ..."
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The past decade has seen an explosion of work on calculi of explicit substitutions. Numerous work has illustrated the usefulness of these calculi for practical notions like the implementation of typed functional programming languages and higher order proof assistants. It has also been shown that eta reduction is useful for adapting substitution calculi for practical problems like higher order uni cation. This paper concentrates on rewrite rules for eta reduction in three dierent styles of explicit substitution calculi: , se and the suspension calculus. Both and se when extended with eta reduction, have proved useful for solving higher order uni cation. We enlarge the suspension calculus with an adequate etareduction which we show to preserve termination and conuence of the associated substitution calculus and to correspond to the etareductions of the other two calculi. We prove that and se as well as and the suspension calculus are non comparable while se is more adequate than the suspension calculus in simulating one step of betacontraction.
SUBSEXPL: A Tool for Simulating and Comparing Explicit Substitutions Calculi ⋆
"... Abstract. We present the system SUBSEXPL used for simulating and comparing explicit substitutions calculi. The system allows the manipulation of expressions of the λcalculus and of three different styles of explicit substitutions: the λσ, the λse and the suspension calculus. Implementations of the ..."
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Abstract. We present the system SUBSEXPL used for simulating and comparing explicit substitutions calculi. The system allows the manipulation of expressions of the λcalculus and of three different styles of explicit substitutions: the λσ, the λse and the suspension calculus. Implementations of the ηreduction are provided for each calculi. Other explicit substitutions calculi can be incorporated into the system easily due to its modular structure. Its applications include: the visualisation of the contractions of the λcalculus, and of guided onestep reductions as well as normalisation via each of the associated substitution calculi. Many useful facilities are available: reductions can be easily recorded and stored into files or Latex outputs and several examples for dealing with arithmetic operations and computational operators such as conditionals and repetitions in the λcalculus are available. The system has been of great help for systematically comparing explicit substitutions calculi, as well as for understanding properties of explicit substitutions such as the Preservation of Strong Normalisation. In addition, it has been used for teaching basic properties of the λcalculus such as: computational adequacy, the importance of de Bruijn’s notation and of making explicit substitutions in real implementations.
SUBSEXPL: A Framework for Simulating and Comparing Explicit Substitutions Calculi A Tutorial
, 2005
"... In this paper we present a framework, called SUBSEXPL, for simulating and comparing explicit substitutions calculi. This framework was developed in Ocaml, a language of the ML family, and it allows the manipulation of expressions of the λcalculus and of several styles of explicit substitutions calc ..."
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Cited by 1 (1 self)
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In this paper we present a framework, called SUBSEXPL, for simulating and comparing explicit substitutions calculi. This framework was developed in Ocaml, a language of the ML family, and it allows the manipulation of expressions of the λcalculus and of several styles of explicit substitutions calculi. Applications of this framework include: the visualisation of the contractions of the λcalculus, and of guided onestep reductions and normalisation via each of the associated substitution calculi. Many useful facilities are available: reductions can be easily recorded and stored into files, latex output and useful examples for dealing with, among other things, arithmetic operations and computational operators such as conditionals and repetitions in the λcalculus. The current implementation of SUBSEXPL includes treatment of three different calculi of explicit substitutions: the λσ, the λse and the suspension calculus; other explicit substitutions calculi can be easily incorporated into the system. An implementation of the ηreduction is provided for each of these explicit substitutions calculi. This system has been of great help for systematically comparing explicit substitutions calculi, as well as for understanding properties of explicit substitutions such as the Preservation of Strong Normalisation. In addition, it has been used for teaching basic properties of the λcalculus such as: computational adequacy, the importance of de Bruijn’s notation and of making explicit substitutions in real implementations based on the λcalculus. Keywords: λCalculus, Explicit Substitutions, Visualisation of β and ηContraction and Normalisation. 1
Term Indexing for the LEOII Prover
"... We present a new term indexing approach which shall support efficient automated theorem proving in classical higher order logic. Key features of our indexing method are a shared representation of terms, the use of partial syntax trees to speedup logical computations and indexing of subterm occurrenc ..."
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We present a new term indexing approach which shall support efficient automated theorem proving in classical higher order logic. Key features of our indexing method are a shared representation of terms, the use of partial syntax trees to speedup logical computations and indexing of subterm occurrences. For the implementation of explicit substitutions, additional support is offered by indexing of bound variable occurrences. A preliminary evaluation of our approach shows some encouraging first results. 1