## The extension theory of Hermitian operators and the moment problem.(English)Zbl 0848.47004

This paper deals with the extension theory of a nondensely defined Hermitian operator in a Hilbert space. Generalized resolvents, preresolvent and resolvent matrices of such an operator are investigated. Necessary and sufficient conditions for a holomorphic operator-valued function to be a preresolvent or resolvent matrix of a Hermitian operator are found. A criterion for an $$R$$-function to be the Weyl function of a Hermitian operator is given. Applications to describe solutions of the truncated Hamburger, Stieltjes and Hausdorff moment problems are given. The results of this paper were partially announced in previous papers of the authors [Dokl. Akad. Nauk Ukr., Ser. A 11, 34-39 (1991); Dokl. Akad Nauk 323, No. 5, 816-822 (1992; Zbl 0820.47007); Dokl. Akad. Nauk 326, No. 1, 12-18 (1992)].

### MSC:

 47A20 Dilations, extensions, compressions of linear operators 47A57 Linear operator methods in interpolation, moment and extension problems 47A56 Functions whose values are linear operators (operator- and matrix-valued functions, etc., including analytic and meromorphic ones) 47B25 Linear symmetric and selfadjoint operators (unbounded)

Zbl 0820.47007
Full Text: