Boundary triplets,weyl functions, and the kreĭn formula

Abstract

This chapter contains a short review of the theory of boundary triplets, and the corresponding Weyl functions, of symmetric operators in Hilbert and Kre?in spaces. The theory of generalized resolvents of such operators is exposed from the point of view of boundary triplets approach. Applications to different continuation problems related to the extension theory of Kre?in space symmetric operators are discussed.