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Topic: Size of ordinal for ordinal definable real
Replies: 8   Last Post: Dec 29, 2013 11:49 AM

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Aatu Koskensilta

Posts: 2,631
Registered: 6/28/08
Re: Size of ordinal for ordinal definable real
Posted: Dec 29, 2013 4:13 AM
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Peter Percival <peterxpercival@hotmail.com> writes:

> How about "phi(x,alpha) is a formula of ZFC such that for each real x
> there is an ordinal alpha such that phi(x,alpha) is true (in V) of
> just that x."


A fine notion as any -- but not as it happens what is in fact
standardly meant in set theory when we say a set, a real, say, is
ordinal definable.

--
Aatu Koskensilta (aatu.koskensilta@uta.fi)

"Wovon man nicht sprechen kann, darüber muss man schweigen"
- Ludwig Wittgenstein, Tractatus Logico-Philosophicus



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