Re: Are Logicians Naturally Logical?

On Tue, 29 Nov 2005 15:54:20 +0100, G. Frege <nomail@invalid> wrote:

Sorry, some typos. Corrected.

>>>
>>> (A -> B) -> ((A -> ~B) -> ~A)
>>>
> Corresponds to a certain form of ~I (or "RAA"):
> ^^^
> [A] [A]
> : :
> B ~B
> : :
> ~B B
> : :
> --- ---
> ~A ~A
>
> (Note that in Gentzen's original systems of ND there are t w o rules
> ~I and ~E to the same effect.)
> ^^^ ^^^
>


F.

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.

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