Algebraic and Analytic Geometry
《Algebraic and Analytic Geometry》 · 第 313 页 · Section 5.4「Invariant Subspaces and the Cayley–Hamilton Theorem」，定义段
Let $T$ be a linear operator on a vector space $V$. A subspace $W$ of $V$ is called a $T$-invariant subspace of $V$ if $T(W)\subseteq W$, that is, if $T(v)\in W$ for all $v\in W$.