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THE HERBRAND FUNCTIONAL INTERPRETATION OF THE DOUBLE NEGATION SHIFT

Published online by Cambridge University Press:  19 June 2017

MARTÍN ESCARDÓ
Affiliation:
SCHOOL OF ELECTRONIC ENGINEERING AND COMPUTER SCIENCE QUEEN MARY UNIVERSITY OF LONDON LONDON, UK E-mail: [email protected]
PAULO OLIVA
Affiliation:
SCHOOL OF COMPUTER SCIENCE UNIVERSITY OF BIRMINGHAM BIRMINGHAM, UKE-mail: [email protected]

Abstract

This paper considers a generalisation of selection functions over an arbitrary strong monad T, as functionals of type $J_R^T X = (X \to R) \to TX$. It is assumed throughout that R is a T-algebra. We show that $J_R^T$ is also a strong monad, and that it embeds into the continuation monad $K_R X = (X \to R) \to R$. We use this to derive that the explicitly controlled product of T-selection functions is definable from the explicitly controlled product of quantifiers, and hence from Spector’s bar recursion. We then prove several properties of this product in the special case when T is the finite powerset monad ${\cal P}_{\rm{f}} \left( \cdot \right)$. These are used to show that when $TX = {\cal P}_{\rm{f}} \left( X \right)$ the explicitly controlled product of T-selection functions calculates a witness to the Herbrand functional interpretation of the double negation shift.

Type
Articles
Copyright
Copyright © The Association for Symbolic Logic 2017 

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