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The Gandy-Hyland functional and a computational aspect of Nonstandard Analysis

Sam Sanders (UGent)
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Abstract
In this paper, we highlight a new computational aspect of Nonstandard Analysis relating to higher-order computability theory. In particular, we prove that the Gandy-Hyland functional equals a primitive recursive functional involving nonstandard numbers inside Nelson's internal set theory. From this classical and ineffective proof in Nonstandard Analysis, a term from Godel's system T can be extracted which computes the Gandy-Hyland functional in terms of a modulus-of-continuity functional and the special fan functional. We obtain several similar relative computability results not involving Nonstandard Analysis from their associated nonstandard theorems. By way of reversal, we show that certain relative computability results, called Herbrandisations, also imply the nonstandard theorem from whence they were obtained. Thus, we establish a direct two-way connection between the field Computability (in particular theoretical computer science) and the field Nonstandard Analysis.
Keywords
Gandy-Hyland functional, Nonstandard Analysis, higher-order, computability theory

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MLA
Sanders, Sam. “The Gandy-Hyland Functional and a Computational Aspect of Nonstandard Analysis.” COMPUTABILITY-THE JOURNAL OF THE ASSOCIATION CIE, vol. 7, no. 1, 2018, pp. 7–43, doi:10.3233/COM-170074.
APA
Sanders, S. (2018). The Gandy-Hyland functional and a computational aspect of Nonstandard Analysis. COMPUTABILITY-THE JOURNAL OF THE ASSOCIATION CIE, 7(1), 7–43. https://doi.org/10.3233/COM-170074
Chicago author-date
Sanders, Sam. 2018. “The Gandy-Hyland Functional and a Computational Aspect of Nonstandard Analysis.” COMPUTABILITY-THE JOURNAL OF THE ASSOCIATION CIE 7 (1): 7–43. https://doi.org/10.3233/COM-170074.
Chicago author-date (all authors)
Sanders, Sam. 2018. “The Gandy-Hyland Functional and a Computational Aspect of Nonstandard Analysis.” COMPUTABILITY-THE JOURNAL OF THE ASSOCIATION CIE 7 (1): 7–43. doi:10.3233/COM-170074.
Vancouver
1.
Sanders S. The Gandy-Hyland functional and a computational aspect of Nonstandard Analysis. COMPUTABILITY-THE JOURNAL OF THE ASSOCIATION CIE. 2018;7(1):7–43.
IEEE
[1]
S. Sanders, “The Gandy-Hyland functional and a computational aspect of Nonstandard Analysis,” COMPUTABILITY-THE JOURNAL OF THE ASSOCIATION CIE, vol. 7, no. 1, pp. 7–43, 2018.
@article{01GRBNXX6K19HWKC2ZK0VRMKGB,
  abstract     = {{In this paper, we highlight a new computational aspect of Nonstandard Analysis relating to higher-order computability theory. In particular, we prove that the Gandy-Hyland functional equals a primitive recursive functional involving nonstandard numbers inside Nelson's internal set theory. From this classical and ineffective proof in Nonstandard Analysis, a term from Godel's system T can be extracted which computes the Gandy-Hyland functional in terms of a modulus-of-continuity functional and the special fan functional. We obtain several similar relative computability results not involving Nonstandard Analysis from their associated nonstandard theorems. By way of reversal, we show that certain relative computability results, called Herbrandisations, also imply the nonstandard theorem from whence they were obtained. Thus, we establish a direct two-way connection between the field Computability (in particular theoretical computer science) and the field Nonstandard Analysis.}},
  author       = {{Sanders, Sam}},
  issn         = {{2211-3568}},
  journal      = {{COMPUTABILITY-THE JOURNAL OF THE ASSOCIATION CIE}},
  keywords     = {{Gandy-Hyland functional,Nonstandard Analysis,higher-order,computability theory}},
  language     = {{eng}},
  number       = {{1}},
  pages        = {{7--43}},
  title        = {{The Gandy-Hyland functional and a computational aspect of Nonstandard Analysis}},
  url          = {{http://doi.org/10.3233/COM-170074}},
  volume       = {{7}},
  year         = {{2018}},
}

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