[alainbryden]

The series of logic fails here:

Gor. No black-white is rough? Soc. None.
Gor. All black-white, then, is non-rough? Soc. Yes.

The answer is not yes to the second statement, because the existance of black-white is exclusive in the first statement and inclusive in the second statement, so you cannot say that one being false results in the other being true. The presumption of black-white being non-existant still stands, so the answer to the second question is No. Try again Gorgias.