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math.SP2024
Weak Coupling and Spectral Instability for Neumann Laplacians
Jussi Behrndt, Fritz Gesztesy, Henk de Snoo
We prove an abstract criterion on spectral instability of nonnegative selfadjoint extensions of a symmetric operator and apply this to self-adjoint Neumann Laplacians on bounded Li…
math.FA2024
Friedrichs and Kre\uın type extensions in terms of representing maps
Seppo Hassi, Henk de Snoo
A semibounded operator or relation in a Hilbert space with lower bound has a symmetric extension $S_{\rm f}=S {\, \widehat + \,} (\{0\} \times {\rm mul\,} S…