[FOM] Deflationism and the Godel phenomena

Jeffrey Ketland ketland at ketland.fsnet.co.uk
Tue Feb 15 21:58:54 EST 2005

Jeffrey Ketland
>> I noted that Tr(PA) is equivalent to ACA.

Harvey Friedman:
> What does the word "equivalent" mean here?

You can interpret Tr(PA) into ACA and vice versa.

> What does "Tr(PA)" mean here?

This is the notation from Feferman's 1991 "Reflecting on Incompleteness" 
paper. He calls it the "ordinary truth theory". It is PA, with Tarski's 
truth axioms for a new predicate T(x), and full induction on the language 
with the predicate T(x).

--- Jeff

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