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Conservation and Uniform Normalization in Lambda Calculi With Erasing Reductions
, 2002
"... For a notion of reduction in a #calculus one can ask whether a term satises conservation and uniform normalization. Conservation means that singlestep reductions of the term preserve innite reduction paths from the term. Uniform normalization means that either the term will have no reduction path ..."
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For a notion of reduction in a #calculus one can ask whether a term satises conservation and uniform normalization. Conservation means that singlestep reductions of the term preserve innite reduction paths from the term. Uniform normalization means that either the term will have no reduction paths leading to a normal form, or all reduction paths will lead to a normal form.
Proving Properties of Typed λTerms Using Realizability, Covers, and Sheaves
, 1995
"... The main purpose of this paper is to take apart the reducibility method in order to understand how its pieces t together, and in particular, to recast the conditions on candidates of reducibility as sheaf conditions. There has been a feeling among experts on this subject that it should be possible ..."
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The main purpose of this paper is to take apart the reducibility method in order to understand how its pieces t together, and in particular, to recast the conditions on candidates of reducibility as sheaf conditions. There has been a feeling among experts on this subject that it should be possible to present the reducibility method using more semantic means, and that a deeper understanding would then be gained. This paper gives mathematical substance to this feeling, by presenting a generalization of the reducibility method based on a semantic notion of realizability which uses the notion of a cover algebra (as in abstract sheaf theory). A key technical ingredient is the introduction a new class of semantic structures equipped with preorders, called preapplicative structures. These structures need not be extensional. In this framework, a general realizability theorem can be shown. Kleene's recursive realizability and a variant of Kreisel's modi ed realizability both t into this framework. We are then able to prove a metatheorem which shows that if a property of realizers satis es some simple conditions, then it holds for the semantic interpretations of all terms. Applying this theorem to the special case of the term model, yields a general theorem for proving properties of typedterms, in particular, strong normalization and con uence. This approach clari es the reducibility method by showing that the closure conditions on candidates of reducibility can be viewed as sheaf conditions. The above approach is applied to the simplytypedcalculus (with types!,,+,and?), and to the secondorder (polymorphic)calculus (with types! and 82), for which it yields a new theorem.
A normalization proof for MartinLöf's type theory
, 1996
"... The theory we will be concerned with in this paper is MartinLöf's polymorphic type theory with intensional equality and the universe of small sets. We will give a different proof of normalization for this theory. ..."
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The theory we will be concerned with in this paper is MartinLöf's polymorphic type theory with intensional equality and the universe of small sets. We will give a different proof of normalization for this theory.