Advanced Linear Algebra
《Advanced Linear Algebra》 · 第 296 页 · Chapter 11「Witt's Theorem」，Theorem 11.36
Let $V$ be a nonsingular orthogonal geometry over a field $F$ with $\operatorname{char}(F)\ne2$. All maximal totally degenerate subspaces of $V$ have the same dimension; this common dimension is called the Witt index of $V$ and is denoted by $i(V)$.