I.  On Fri Oct 5 23:35:03 EDT 2007 Finnur Larusson  wrote

http://www.cs.nyu.edu/pipermail/fom/2007-October/012009.html

         I confirm that Larusson "proof"  under corrections can be formalized in ZFC.

II. On Sun Oct 7 14:12:37 EDT 2007 Timothy Y. Chow  wrote:

http://www.cs.nyu.edu/pipermail/fom/2007-October/012015.html

"In order to deduce "ZFC is inconsistent" from "ZFC |- ~con(ZFC)" one needs

something more than the consistency of ZFC, e.g., that ZFC has an

omega-model (i.e., a model in which the integers are the standard

integers).

To put it another way, why should we "believe" a statement just because

there's a ZFC-proof of it?  It's clear that if ZFC is inconsistent, then

we *won't* "believe" ZFC-proofs.  What's slightly more subtle is that the

mere consistency of ZFC isn't quite enough to get us to believe

arithmetical theorems of ZFC; we must also believe that these arithmetical

theorems are asserting something about the standard naturals.  It is

"conceivable" that ZFC might be consistent but that the only models it has

are those in which the integers are nonstandard, in which case we might

not "believe" an arithmetical statement such as "ZFC is inconsistent" even

if there is a ZFC-proof of it.

So you need to replace your initial statement that "we assume throughout

that ZFC is consistent" to "we assume throughout that ZFC has an

omega-model"; then you should see that your "paradox" dissipates.".

J.Foukzon.Remark1. Let Mst  be  an  omega-model  of  ZFC  and let ZFC[Mst]  be a  ZFC with a quantifiers bounded on model Mst. Then easy to see that  Larusson  "paradox"  valid inside  ZFC[Mst] 

III.  On Wed Oct 10 14:12:46 EDT 2007 Richard Heck wrote:

http://www.cs.nyu.edu/pipermail/fom/2007-October/012035.html

Or, more directly, what you need is reflection for ZFC: Bew_{ZFC}(A) -->

A. And that of course is not available in ZFC, by L"ob's theorem.

J.Foukzon.Remark2 However such reflection is .available in ZFC[Mst] by standard interpretation of Bew_{ZFC}(A) in omega-model  Mst    

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