103 citations · 129 across the 29 of their papers we have counts for
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math.SP2008
On Symmetries in the Theory of Finite Rank Singular Perturbations
Seppo Hassi, Sergii Kuzhel
For a nonnegative self-adjoint operator acting on a Hilbert space singular perturbations of the form are studie…
math.SP2006★ 103 cited
Boundary relations and generalized resolvents of symmetric operators
Vladimir Derkach, Seppo Hassi, Mark Malamud +1
The Kre\uın-Naimark formula provides a parametrization of all selfadjoint exit space extensions of a, not necessarily densely defined, symmetric operator, in terms of maximal dissi…
math.SP2005
A general realization theorem for matrix-valued Herglotz-Nevanlinna functions
Sergey Belyi, Seppo Hassi, Henk de Snoo +1
New special types of stationary conservative impedance and scattering systems, the so-called non-canonical systems, involving triplets of Hilbert spaces and projection operators, a…