L (λ)= λnAn+ λn− 1An− 1+···+ A0,(1) where the Ak are operators acting in a Hilbert space
and λ∈ C is the spectral parameter. In the simplest case L (λ)= λI− A, where I is the identity …

A symmetric Nevanlinna function Q is of the form Q (z)= zQs (z2) where Qs and Q 0 (z)= zQs
(z) are also Nevanlinna functions. In such a situation Qs and–Q–10 are Stieltjes functions …

Additive decompositions of a meromorphic function give rise to quotient representations of a
particular form. We raise the question which quotient representations of a given function …

Abstract We consider (2× 2)-Hamiltonian systems of the form y'(x)= zJH (x) y (x), x∊[s−, s+). If
a system of this form is in the limit point case, an analytic function is associated with it …

We investigate the structure of a maximal chain of matrix functions whose Weyl coefficient
belongs to N _ κ^+. It is shown that its singularities must be of a very particular type. As an …

We investigate a particular subclass of so-called symmetric indefinite Hermite-Biehler
functions and give a characterization of functions of this class in terms of the location of their …

By a Hamiltonian, we understand a function H defined on a (possibly unbounded)
interval.(a, b), which takes real and non-negative. 2× 2-matrices as values, is locally …

We present two inverse spectral relations for canonical differential equations Jy′(x)=-zH (x)
y (x), x∈[0, L): Denote by QH the Titchmarsh–Weyl coefficient associated with this equation …

The subclasses N κ (∞) of the classes N κ of generalized Nevanlinna functions appear in
the context of Pontryagin space models, where they correspond to model relations having a …

We define and investigate the class of symmetric and the class of semibounded de Branges
spaces of entire functions. A construction is made which assigns to each symmetric de …