Re: Derivations (SD)

"1st Semester Logic Student" <jzarwel@xxxxxxxxx> writes:

> d. {A -> B, B -> C, ~C} |- ~A
>
> Couldn't A be derived from A -> B with horseshoe elimination and then
> just slap the tilde on the A with negation introduction? I think I'm
> missing something here.

Let's see, you're assuming a rule called "horseshoe elimination" by
which A follows from A->B, and a rule called "negation introduction"
by which ~A follows from A. That must be an interesting text you're
using.

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