Borel Determinacy and Metamathematics

Borel determinacy states that if G(T;X) is a game and X is Borel, then G(T;X) is determined. Proved by Martin in 1975, Borel determinacy is a theorem of ZFC set theory, and is, in fact, the best determinacy result in ZFC. However, the proof uses sets of high set theoretic type (N1 many power sets of ω). Friedman proved in 1971 that these sets are necessary by showing that the Axiom of Replacement is necessary for any proof of Borel Determinacy. To prove this, Friedman produces a model of ZC and a Borel set of Turing degrees that neither contains nor omits a cone; so by another theorem of Martin, Borel Determinacy is not a theorem of ZC. This paper contains three main sections: Martin's proof of Borel Determinacy; a simpler example of Friedman's result, namely, (in ZFC) a coanalytic set of Turing degrees that neither contains nor omits a cone; and finally, the Friedman result.

Grantor dc:publisher

University of North Texas

Year dc:date

2001

Author dc:creator

• Bryant, Ross

Contributors dc:contributor

• Jackson, Stephen C.
• Brand, Neal

• Descriptive set theory.
• Metamathematics.
• Borel Determinacy
• set theory
• ZFC
• ZC
• game theory

Statement dc:rights

• Public
• Copyright
• Bryant, Ross David
• Copyright is held by the author, unless otherwise noted. All rights reserved.

Language dc:language

English

Identifier

oclc: 51977978
https://digital.library.unt.edu/ark:/67531/metadc3061/
ark: ark:/67531/metadc3061

OAI identifier oai:identifier

info:ark/67531/metadc3061