Let $V$ be a finite dimensional vector space over a field $K$ of characteristic zero, and let $T \in End(V)$. A subspace $W \subseteq V$ is $T$-invariant if $T(W) \subseteq W$; and $W$ is $T$-irreducible if it is T-invariant and the only T-invariant subspaces of $W$ are $0$ and $W$.
(a) Suppose that $T \in End(V)$ has order $n$ in $End(V)$ under composition, and that $W \subseteq V$ is a T-invariant subspace, Show that $W$ has a T-invariant complement $W'$.
(b). Under the hypotheses of $(a)$, show that $V$ can be written as the direct product of T-irreducible subspaces.
(c). What if $T$ does not have finite order in $End(V)$?
(d). What if $K$ does not have characteristic zero?
I was able to prove parts (a) and (b). However, I am not so sure about parts (c) and (d). Since my proof of parts (a) and (b) relied on the fact that $T$ had finite order and $K$ had characteristic zero, I assume that the results no longer hold. This all seems similar to to Maschke's theorem, but I am not familiar with representation theory.
