nondegenerate bilinear form

《Advanced Linear Algebra》 · 第 266 页 · Chapter 11「Degeneracy and Nonsingularity」

1) A vector $v\in V$ is degenerate if $v\in V^\perp$. The set $V^\perp$ of all degenerate vectors is called the radical of $V$ and denoted by $\operatorname{rad}(V)$. … 2) $V$ is nonsingular, or nondegenerate, if $\operatorname{rad}(V)=\{0\}$.