FOM: Banach-Tarski and Borel sets
kanovei at wminf2.math.uni-wuppertal.de
Thu Dec 11 14:00:16 EST 1997
> There is a larger question here: how is TBU meant to be used? One
>can restrict one's attention to Borel sets in the contexts where it is
>appropriate to do so without having a formal theory like TBU around.
>People have been doing it for the last 100 years or so.
Perhaps the full strength of 2nd order PA can be not
necessary to develop such a theory, a kind of
"Borel PA-2" or perhaps "Delta^1_2 PA-2" will work,
however this is perhaps not so nice as Feferman's
reduction to PA itself.
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