“This monograph is a comprehensive tour de force on the theory of boundary triplets and their Weyl functions … with an eye on applications to boundary value problems for differential equations. … The bibliography is extensive (784 entries); the connection of each reference to the topics discussed in the text is elaborated in the supplementary notes at the end of each chapter. The book is very well written and carefully crafted; the exposition is amenable … .” (Julio H. Toloza, Mathematical Reviews, April, 2022)

• Linear relations.- Boundary triplets and Weyl functions.- Spectra and Weyl functions.- Operator models.- Nonnegative selfadjoint extensions.- Sturm-Liouville operators.- Canonical systems.- Schrodinger operators.- Sums of closed subspaces in a Hilbert space.- Factorization of bounded linear operators.- Integral representations of Carathéodory functions.- The integral representation of Nevanlinna functions.

“This monograph is a comprehensive tour de force on the theory of boundary triplets and their Weyl functions … with an eye on applications to boundary value problems for differential equations. … The bibliography is extensive (784 entries); the connection of each reference to the topics discussed in the text is elaborated in the supplementary notes at the end of each chapter. The book is very well written and carefully crafted; the exposition is amenable … .” (Julio H. Toloza, Mathematical Reviews, April, 2022)

• Linear relations.- Boundary triplets and Weyl functions.- Spectra and Weyl functions.- Operator models.- Nonnegative selfadjoint extensions.- Sturm-Liouville operators.- Canonical systems.- Schrodinger operators.- Sums of closed subspaces in a Hilbert space.- Factorization of bounded linear operators.- Integral representations of Carathéodory functions.- The integral representation of Nevanlinna functions.