Transition of the Quasi-Levels in the Discrete Spectrum of the Schrödinger Operator under Strong Perturbations of the Potential -- A Criterion for the Existence of the Complete Wave Operators in the Theory of Scattering with Two Spaces -- The Inverse Problem for the Wave Equation with an Unknown Source -- On the Various Formulations of the One-Dimensional Inverse Problem for the Telegraph Equation -- Quantitative Characteristics of Singular Measures -- Spectral Identities and the Trace Formula in the Friedrichs Model -- Perturbation of the Spectrum of the One-Dimensional Self-Adjoint Schrödinger Operator with a Periodic Potential -- The Field of a Point Source Located Outside a Convex Curve -- Criteria for the Boundedness and Complete Continuity of Certain Imbedding Operators -- A Uniqueness Theorem for Functions with Positive Imaginary Part -- Application of the Method of Standard Comparison Problems to Perturbations of the Coulomb Field. The Discrete Spectrum.