[FOM] computable numbers, independent freindly logic

Aatu Koskensilta aatu.koskensilta at xortec.fi
Sat Dec 27 17:03:23 EST 2003

George Kapoulas wrote:

>2) There is an approach for logic 
>called independent friendly logic.
>Does anyone know  if there is 
>proof that the approach used by 
>this logic  cannot be expressed 
>in 1st order logic, 
>and references for this?
It's not entirely clear what "the approach used by this logic"
means. However, it's well known that the expressive power of
IF-logic (independence friendly) equals that of the Sigma^1_1
fragment of second order logic. An easy-going introduction to
these issues - along with more philosophical musings - can be
found in Jaakko Hintikka's Philosophy of Mathematics Revisited.

Aatu Koskensilta (aatu.koskensilta at xortec.fi)

"Wovon man nicht sprechen kann, daruber muss man schweigen"
 - Ludwig Wittgenstein, Tractatus Logico-Philosophicus

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