Feferman–Schütte ordinal

In mathematics, the Feferman–Schütte ordinal Γ0 is a large countable ordinal. It is the proof-theoretic ordinal of several mathematical theories, such as arithmetical transfinite recursion. It is named after Solomon Feferman and Kurt Schütte.

It is sometimes said to be the first impredicative ordinal,[1][2] though this is controversial, partly because there is no generally accepted precise definition of "predicative". Sometimes an ordinal is said to be predicative if it is less than Γ0.

There is no standard notation for ordinals beyond the Feferman–Schütte ordinal. There are several ways of representing the Feferman–Schütte ordinal, some of which use ordinal collapsing functions: , or .

Definition

The Feferman–Schütte ordinal can be defined as the smallest ordinal that cannot be obtained by starting with 0 and using the operations of ordinal addition and the Veblen functions φα(β). That is, it is the smallest α such that φα(0) = α.

gollark: Also, the sun will eventually do bad things.
gollark: Technically, solar panels have a finite lifespan and we can't make arbitrarily many from Earth resources.
gollark: I mean, it's less renewable than solar.
gollark: I can have the GTech™ Mercury assembler swarms self-replicate and disassemble it if you want?
gollark: It would be cool™ and probably fix some problems to have nuclear-heated desalination plants.

References
  1. Kurt Schütte, Proof theory, Grundlehren der Mathematischen Wissenschaften, Band 225, Springer-Verlag, Berlin, Heidelberg, New York, 1977, xii + 302 pp.
  2. Solomon Feferman, "Predicativity" (2002)
  • Pohlers, Wolfram (1989), Proof theory, Lecture Notes in Mathematics, 1407, Berlin: Springer-Verlag, doi:10.1007/978-3-540-46825-7, ISBN 3-540-51842-8, MR 1026933
  • Weaver, Nik (2005), Predicativity beyond Gamma_0, arXiv:math/0509244, Bibcode:2005math......9244W
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.