つづき

7. A proof of Fermat’s Last Theorem in PA?
We have founded the whole SGA for arbitrary sites, while individual proofs in number theory use only low degree cohomology of sites close to arithmetic.
Detailed bounds may suffice to get existing proofs into n-order arithmetic for relatively low n, as in Section 3.8.4. That might be a good context for such hard logical analysis as Macintyre (2011) begins for FLT.
More work might bound the constructions within a conservative extension of PA (Takeuti, 1978) to show some existing proof of FLT works essentially in PA.
It might help further reduce the proof to Exponential Function Arithmetic (EFA) as conjectured in (Friedman, 2010).
Such estimates are likely to be difficult.
This is no logical end run around serious arithmetic.
Not motivated by concern with logic, Kisin (2009b) extends and simplifies (Wiles, 1995), generally using geometry less than commutative algebra, visibly reducing the demands on set theory. And Kisin (2009a) completes a different proof of FLT by a strategy of Serre advanced by Khare and Wintenberger.

References
Takeuti, G. (1987). Proof Theory. Elsevier Science Ltd, 2nd edition.
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