FOM: Re: your FOM posting on proof theory
wtait@ix.netcom.com
wtait at ix.netcom.com
Mon Jul 20 17:23:37 EDT 1998
Jeremy,
I have been enjoying your discussion of proof theory. But a small remark
about:
>The idea is this: the stronger a theory is, the more recursive ordinals it
>"knows about," i.e. the more powerful the transfinite induction
>principles it can derive. So determining this ordinal measures, in a
>sense, the strength of the theory.
That is the idea; but of course, as you know, the proof theoretic ordinal
is too crude a measure. T+Consis_T---or, indeed, T+\phi, where \phi is
any true sigma^1_1 sentence---will have the same proof theoretic ordinal
as T.
Incidently, although I received your posting in reply to Neil, I did not
receive the posting of Neil's from which you quoted.
Bill Tait
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