Talk:Borel determinacy theorem

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[edit] Friedman's theorem

"Friedman's theorem of 1971 showed that there is no countable ordinal δ such that V_δ satisfies Borel determinacy."

This doesn't seem right; isn't Borel determinacy a statement about the existence or nonexistence of sets living in V_ω+ω, so that if you start with a model of ZFC then V_δ will satisfy Borel determinacy for any δ≥ω+ω? I looked up Friedman's theorem, and it seems that what he actually does is construct a different model L^ω+ω, related to the constructible universe, which satisfies Z but not Borel determinacy.

Michael Shulman (talk) 21:06, 8 March 2008 (UTC)