- Research Article
37
- 10.1016/j.tcs.2019.01.015
Canonicity and normalization for dependent type theory
- Jan 15, 2019
- Theoretical Computer Science
- Thierry Coquand
Canonicity and normalization for dependent type theory
In 1930, A. Heyting first specified a formal system for part of intuitionistic mathematics. Although his rules were presumably motivated by the “intended interpretation” or meaning of the logical symbols, over the years a number of other possible interpretations have been discovered for which the rules are also valid. In particular, one might mention the realizablity interpretation of Kleene, the (Dialectica) interpretation of Gödel, and various semantic interpretations, such as Kripke models. (Each of these has several variants or close relatives.) Each such interpretation can be regarded as defining precisely a certain “notion of constructivity”, the study of which may illuminate the still rather vague notions which underlie the intended interpretation; or, if one doubts that there is a single interpretation “intended” by all constructivist mathematicians, the study of precisely defined interpretations may help to delineate and distinguish the possibilities.In the last few years, Heyting's systems have been vastly extended, in order to encompass the large and growing body of constructive mathematics. Several kinds of new systems have been put forward and studied. The present author has extended the various realizability interpretations to several of these systems [B1], [B2] and drawn a number of interesting applications. The mathematical content of the present paper is an interpretation in the style of Godel's Dialectica interpretation, but applicable to the new systems put forward by Feferman [Fl]. The original motivation for this work was to obtain certain metamathematical applications: roughly speaking, Markov's rule and its variants.
Canonicity and normalization for dependent type theory
Canonicity and normalization for dependent type theory
Cartesian closed Dialectica categories
Cartesian closed Dialectica categories
Semantic interpretation as higher-order deduction
Traditional accounts of the semantic interpretation of quantified phrases and its interaction with reference and ellipsis have relied on formal manipulations of logical forms (quantifier raising) or complicated denotations for phrases (Cooper storage). These complications are one of the motivations for the development of categorial semantic theories. However, these theories appear to face their own difficulties in accounting for the full range of scoping possibilities in natural language, and have been losing some of their original elegance. Experiments suggest that the insights of the traditional theories may be revived in a semantically more respectable form by taking advantage of the abstraction mechanisms of higher-order hereditary Harrop formulae, as implemented in λProlog, to represent scoping and extraction dependencies without the need for formal conditions on logical forms or elaborate denotations for phrases. The technique used is an adaptation of a method of Felty and Miller for dispensing with side conditions in sequent-calculus rules. Finally, it will be seen that this approach is after all a close relative of categorial semantics.
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