Let $T$ be a delta endomorphism of $\mathbb{K}[X]$. Show that there exists a sequence of scalars $\left(\alpha_k\right)_{k \in \mathbb{N}}$ satisfying $\alpha_0 = 0$, $\alpha_1 \neq 0$ and $T = \sum_{k=1}^{+\infty} \alpha_k D^k$.
Let $T$ be a delta endomorphism of $\mathbb{K}[X]$.
Show that there exists a sequence of scalars $\left(\alpha_k\right)_{k \in \mathbb{N}}$ satisfying $\alpha_0 = 0$, $\alpha_1 \neq 0$ and $T = \sum_{k=1}^{+\infty} \alpha_k D^k$.