Abstract
In this paper, we investigate the invariance properties, i.e. robustness, of phenomena related to the notions of algorithm, finite procedure and explicit construction. First of all, we provide two examples of objects for which small changes completely change their (non)computational behavior. We then isolate robust phenomena in two disciplines related to computability.
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Notes
- 1.
See (Freer et al. 2011).
- 2.
The words in italics have precise technical definitions to be found in e.g. (Soare 1987).
- 3.
This explains why, in any real-world scenario invariably involving noise, the non-computability of P[Y | X] never manifests itself.
- 4.
- 5.
See (Hacking1983, pp. 54-55), (Salmon 1984, pp. 214-220) and (Salmon 1998, pp. 87-88).
- 6.
In light of Examples 1 and 2, we may rest assured that intermediate values and conditional probabilities will always be computable in practice, as actual computational practice suggests.
- 7.
See (Church 1936) and (Turing 1937). Intuitively, a Turing machine is an idealized computer with no limits on storage and meomory.
- 8.
See (Friedman 1975; 1976).
- 9.
See (Simpson 2009) for an introduction to Reverse Mathematics and p. xiv for the quote.
- 10.
See (Simpson 2009, Theorem I.10.3).
- 11.
Thus, Reverse Mathematics is intimately tied to Recursion Theory and computability.
- 12.
In particular, Weak König’s Lemma states the existence of an infinite path through an infinite binary tree. Even for computable infinite binary trees, the infinite path need not be computable. In other words, WKL is false for the recursive/computable sets. See (Simpson 2009).
- 13.
See (Sanders 2011) for an introduction to ERNA and a proof of Theorem 3.
- 14.
In particular, ERNA was introduced around 1995 by Sommer and Suppes to formalize mathematics in physics. See (Sommer and Suppes 1996; 1997).
- 15.
For an introduction to Nonstandard Analysis, we refer to (Kanovei and Reeken 2004).
- 16.
In ERNA, the Riemann integral is only defined up to infinitesimals.
- 17.
A similar (and equally valid) principle is If RCA 0 ⊢ T(=), then ERNA ⊢ T(≈).
- 18.
A similar principle is If RCA0 ⊢ T( = ), then ERNA + ∏2-TRANS ⊢ T(≋).
- 19.
The first one is the removing of parameters in ∏ 1-TRANS and the second one is the assumption of a greatest relevant infinite element.
- 20.
The title of this section is explained in Remark 16 below. The italicized concepts are introduced in Section 3.2.
- 21.
See (Kreisler 2006).
- 22.
See (Soare 1987, Lemma 3.2.)
- 23.
The function (μk ≤ m)ψ(k) computes the least k ≤ m such that ψ(k), for ψ in Δ0. It is available in most logical systems.
- 24.
See (van Heijenoort 1967) and (Bishop 1967).
- 25.
See (Bridges 1999, p. 96) and (Richman 1990).
- 26.
These results are taken from (Ishihara 2006).
- 27.
See (Bishop 1967) or (Ishihara 2006).
- 28.
Note that we use the word ‘translation’ informally: The definition of \(\mathbb{V}\) is inspired by the intuitionistic disjunction, but that is the only connection.
- 29.
See (Sanders 2012) for a list of thirty translated theorems.
- 30.
See e.g. (Bridges 1999, Axiom set R2).
- 31.
- 32.
With the notable exception of Erik Palmgren in e.g. (Palmgren 2001).
- 33.
See (Wattenberg 1988).
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Sanders, S. (2013). On Algorithm and Robustness in a Non-standard Sense. In: Andersen, H., Dieks, D., Gonzalez, W., Uebel, T., Wheeler, G. (eds) New Challenges to Philosophy of Science. The Philosophy of Science in a European Perspective, vol 4. Springer, Dordrecht. https://doi.org/10.1007/978-94-007-5845-2_9
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