1. Interpolation Spaces
2. On the Spectrum of Singular Boundary - Value Problems;Birman;Mat. Sb,1961
3. Discrete Spectrum in the Gaps of a Continuous One for Perturbations with Large Coupling Constant;Birman;Advances in Soviet Math.,1991
4. On the Asymptotics of the Discrete Spectrum for Certain Singular Differential Operators;Birman;Probl. Math. Fiz.