>>2. I have no patience with your link. He used calculus to
>>argue that
>>
>>F(x,y) ¡Ý 0
>>
>>while it is obvious from the definition.
>
>I need help on this. Did you mean that the statement was
>unnecessary, or that it depends on the PT and creates a
>circular argument?

No, it is exactly as I wrote. He defined F(x, y) which is by defintion is not negative and then wasted a page proving that it is so by using calculus. There is not circularity but a waste.

>Also, I did post that proof on mathforum... And the
>discussion there got me to thinking that I should not assume
>that slope of a line can be gained apart from the PT.

Just continue the discussion there.