[FOM] Recursion Theory and Goedel's theorems
Arnon Avron
aa at tau.ac.il
Wed Aug 1 05:17:19 EDT 2007
On Tue, Jul 24, 2007 at 10:42:20AM -0700, H. Enderton wrote:
> Maybe it's not clear that this undecidable sentence is Pi^0_1.
> But I still advance the claim that the heart of the
> first incompleteness theorem lies in recursion theory.
I am not sure. First, the fact that the undecidable sentence
is Pi^0_1 is very important - these are the sentences
which are mechanically refutable in case they are false.
More important: Goedel's proof includes a procedure which
given an r.e. true theory, provides a true sentence
(which we know to be true if we know that the theory is true!)
which is undecidable in that theory. For me this is a
positive part of the first incompleteness theorem which
is no less important than the negative part. Does recursion
theory provide such a procedure too?
Arnon Avron.
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