@article{Khrabustovsky_2006, place={Харків, Україна}, title={On the Characteristic Operators and Projections and on the Solutions of Weyl Type of Dissipative and Accumulative Operator Systems. II. Abstract Theory}, volume={2}, url={http://jmag.ilt.kharkov.ua/index.php/jmag/article/view/jm02-0299e}, abstractNote={Special maximal semi-definite subspaces (maximal dissipative and accumulative relations) are considered. Particular cases of those arise in studying boundary problems for systems mentioned in the title. We provide a description of such subspaces and list their properties. A criterion is found that condition of semi-definiteness of sum of indefinite quadratic forms reduces to semi-definiteness of each of the summand forms, i.e it is separated. In the case when the forms depend on a parameter $\lambda$ (e.g., a spectral parameter) within a domain $\Lambda \subset \mathbb{C}$, a condition is found under which separation of the semi-definiteness property at a single $\lambda$ implies its separation for all $\lambda$.
Mathematics Subject Classification: 34B07, 34G10, 46C20, 47A06, 47B50.}, number={3}, journal={Журнал математичної фізики, аналізу, геометрії}, author={Khrabustovsky, V. I.}, year={2006}, month={Трав}, pages={299–317} }