[math-fun] The Wittless Duck

I have been struggling to recall a rather surprising theorem, encountered in passing while searching for something unrelated, concerning the structure of quadratic spaces for which the Witt index exceeds 2 . Not only can I not find the theorem; I can't even locate a definition of the Witt index --- that is |p - q| + r , where the (possibly degenerate) quadratic form signature involves p positive, q negative, r absent squares. Can somebody out there please unscramble my brain (or my surfing technique) for me? Dribble, mutter ... Fred Lunnon