= Positive spectrum of a dissipative operator is adjoint point spectrum
{title2=$\alpha\in\sigma(Z)\Longleftrightarrow\alpha\in\sigma_p(Z^*)\quad(\alpha>0)$}
For a closed densely defined <dissipative operator>, the estimate $\|(\alpha I-Z)f\|\geq\alpha\|f\|$ makes its range closed and its kernel trivial. Thus a positive spectral value means this range is proper, which is equivalent to a nonzero vector in $\ker(\alpha I-Z^*)$. Dissipativity is essential: a real multiplication operator may have positive continuous spectrum with no adjoint eigenvector.
// Target: analysis.bigb
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