In this paper, we investigate a detailed treatment of some subsets of essential spectra of a
closed multivalued linear operator. On the following, we will establish some results on …

This paper consists of two parts. In the first part, which is of more abstract nature, the notion
of quasi-boundary triples and associated Weyl functions is developed further in such a way …

One of the central objects in the theory of singular Sturm-Liouville differential expressions is
the Titchmarsh-Weyl function m introduced and studied in the classical works of Titchmarsh …

This paper focuses on spectral properties of self-adjoint subspaces in the product space of a
Hilbert space. Several classifications of the spectrum of a self-adjoint subspace are …

This paper focuses on boundedness and closedness of linear relations, which include both
single-valued and multi-valued linear operators. A new (single-valued) linear operator …

Quasi-Fredholm relations of degree d∈ N in Hilbert spaces are defined in terms of
conditions on their ranges and kernels. They are completely characterized in terms of an …

Multivalued projections are applied to the study of weighted least squares solutions of linear
relations equations (or inclusions) and some of its applications. To this end a matrix …

Boundary relations for a symmetric relation in a Pontryagin space are studied and the
corresponding Weyl families are characterized. In particular, it is shown that every …

A linear relation, ie, a multivalued operator T from a Hilbert space H to a Hilbert space K has
Lebesgue type decompositions TT 1 is a closable operator and T 2 is an operator or relation …

Let ${\mathfrak H} _A $, ${\mathfrak H} _B $, and ${\mathfrak H} $ be Hilbert spaces. Let $ A
$ be a linear relation from ${\mathfrak H} $ to ${\mathfrak H} _A $ and let $ B $ be a linear …