Algebraic Number Theory
《Algebraic Number Theory》 · 第 194 页 · Chapter III，Section 2「Different and Discriminant」，定义段
Let $L/K$ be a finite separable field extension. We are given a canonical nondegenerate symmetric bilinear form on the $K$-vector space $L$, namely the trace form $T(x,y)=\operatorname{Tr}(xy)$.