Assume we have a linear operator $P_0: D->H$ where $D$ is the domain and $H$ some Hilbert space it is acting on. Assume moreover that the spectrum of $P_0$ is purely essential. If $z$ is a complex ...
Is it true that every closed operator on a separable Hilbert H space only has countably many eigenvalues? Or put the other way around, if I want to ensure that a (not necessarily bounded) linear ...