1. The structure of regions of stability for linear canonical systems of differential equations with periodic coefficients;Gel'fand;Usp. mat. Nauk,1955
2. The solution of problems on perturbation in the case of matrices and selfconjugate and non-selfconjugate differential equations;Vishik;Usp. mat. Nauk,1960
3. The analytic properties of multipliers of periodic canonical differential systems of positive type;Krein;Izv. Akad. Nauk SSSR (Series Mat.),1962
4. The theory of analytic functions;Markushevich,1950
5. Basic positions on defective and radical numbers and indices of linear operators;Gokhberg;Usp. mat. Nauk,1957