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Classical truth in higher types

Ulrich Berger Orcid Logo

MLQ, Volume: 54, Issue: 3, Pages: 240 - 246

Swansea University Author: Ulrich Berger Orcid Logo

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DOI (Published version): 10.1002/malq.200710046

Abstract

We study, from a classical point of view, how the truth of a statement about higher type functionals depends on the underlying model. The models considered are the classical set-theoretic finite type hierarchy and the constructively more meaningful models of continuous functionals, hereditarily effe...

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Published in: MLQ
ISSN: 0942-5616 1521-3870
Published: 2008
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URI: https://cronfa.swan.ac.uk/Record/cronfa7436
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Abstract: We study, from a classical point of view, how the truth of a statement about higher type functionals depends on the underlying model. The models considered are the classical set-theoretic finite type hierarchy and the constructively more meaningful models of continuous functionals, hereditarily effective operations, as well as the closed term model of Gödel's system T. The main results are characterisations of prenex classes for which truth in the full set-theoretic model transfers to truth in the other models. As a corollary we obtain that the axiom of choice is not conservative over Gödel's system T with classical logic for closed Sigma-2-formulas. We hope that this study will contribute to a clearer delineation and perception of constructive mathematics from a classical perspective.
Keywords: logic, higher types, constructive mathematics
College: Faculty of Science and Engineering
Issue: 3
Start Page: 240
End Page: 246