1. M. G. Krein, Stability of Solutions of Differential Equations in Banach Spaces [in Russian], Nauka, Moscow (1970).
2. S. G. Krein, Linear Differential Equations in Banach Spaces [in Russian], Nauka, Moscow (1967).
3. A. A. Boichuk, V. F. Zhuravlev, and A. M. Samoilenko, Generalized Inverse Operators and Fredholm Boundary-Value Problems [in Russian], Institute of Mathematics, Ukrainian National Academy of Sciences, Kiev (1995).
4. A. A. Boichuk and A. M. Samoilenko, Generalized Inverse Operators and Fredholm Boundary-Value Problems, VSP, Utrecht (2004).
5. A. A. Boichuk and A. A. Pokutnyi, “Boundary-value problems for differential equations in a Banach space,” Nelin. Kolyvannya, 12, No. 1, 16–19 (2009); English translation: Nonlin. Oscillations, 12, No. 1, 15–18 (2009).