On 4.15. Corollary. Conway's Functional Analysis?

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The following is from Conway's Functional Analysis:

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Why $[\operatorname{ker}(T - A)^*]^\perp = H$?

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Compactness of $T$ implies that of $T^{*}$. Since $\lambda \neq 0$ and $\overline {\lambda} \notin \sigma_p (T^{*})$ it follows from compacteness of $T^{*}$ that $T^{*}-\overline {\lambda}$ is invertible. Hence its kernel is $\{0\}$ and the orthogoanl complement of the kernel is $\mathcal H$.