"The appendix is very valuable and helps the reader to find an orientation in the very voluminous literature devoted to the spectral theory of differential operators ... anybody interested in the spectral theory of differential operators will find interesting information in the book, including formulation of open problems for possible investigation." Mathematical Reviews "This book is well-written, and a list of symbols and the index prove useful. A substantial number of open questions is also included. Although addressed primarily to the research community, the book could also be used as a graduate textbooks." Zentralblatt MATH

• # Relation Between Spectral and Oscillatory Properties for the Matrix Sturm-Liouville Problem # Fundamental System of Solutions for an Operator Differential Equation with a Singular Boundary Condition # Dependence of the Spectrum of Operator Boundary Problems on Variations of a Finite or Semi-Infinite Interval # Relation Between Spectral and Oscillatory Properties for Operator Differential Equations of Arbitrary Order # Self-Adjoint Extensions of Systems of Differential Equations of Arbitrary Order on an Infinite Interval in the Absolutely Indefinite Case # Discrete Levels in Spectral Gaps of Perturbed Schrodinger and Hill Operators

"The appendix is very valuable and helps the reader to find an orientation in the very voluminous literature devoted to the spectral theory of differential operators ... anybody interested in the spectral theory of differential operators will find interesting information in the book, including formulation of open problems for possible investigation." Mathematical Reviews "This book is well-written, and a list of symbols and the index prove useful. A substantial number of open questions is also included. Although addressed primarily to the research community, the book could also be used as a graduate textbooks." Zentralblatt MATH

• # Relation Between Spectral and Oscillatory Properties for the Matrix Sturm-Liouville Problem # Fundamental System of Solutions for an Operator Differential Equation with a Singular Boundary Condition # Dependence of the Spectrum of Operator Boundary Problems on Variations of a Finite or Semi-Infinite Interval # Relation Between Spectral and Oscillatory Properties for Operator Differential Equations of Arbitrary Order # Self-Adjoint Extensions of Systems of Differential Equations of Arbitrary Order on an Infinite Interval in the Absolutely Indefinite Case # Discrete Levels in Spectral Gaps of Perturbed Schrodinger and Hill Operators