Mr Dudley, once again you are confused. Most define angle of attack as
the chord line of a wing, and of course with that definition it can be
negative and still generate lift. Mr Mx chooses a different way of
defining it. It is some angle such that when it goes negative the
airfoil can generate no lift. Do you remember the disbarred former
president Clinton saying something about "It depends on what 'is'
means"?

In Mx's case, words change meaning so that he is NEVER wrong. It must
be an interesting version of English he teaches.

But he does offer amusement for some of us on otherwise humorless
days, doesn't he?