Re: reductio ad falsum versus reductio ad absurdum


Torkel Franzen wrote:
> "futurist" <adamgolding@xxxxxxxxxxxxxxx> writes:
>
> > does A have to be atomic in the first case?
>
> No.
>
> > if A is not atomic, couldn't you have any number of '~' symbols
> > 'inside' the A? (i.e. in the wff that A represents?)
>
> Yes. What is the relevance of this observation?

then you should be able to prove pv~p using either rule.

in the first case you assume A where A <=> ~(Pv~P)
in the secome case you assume ~A where A <=> (Pv~P)

(with <=> meaning formal equivalence here)

the second form seems like the first rule with an unnecessary tilde (~)
added in... am i missing something?

.

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