1. V. A. Ambartsumyan, Scientific Treatise (Yerevan, Izd-vo Akad. Nauk Arm. SSR, 1960), Vol. 1.
2. V. V. Sobolev, Course in Theoretical Astrophysics (National Aeronautics and Space Administration, Washington, D.C., 1969).
3. H. H. Kagivada, R. E. Kalaba, and A. Shumitzky, ‘‘An initial-value method for Fredholm equations,’’ J. Math. Anal. Appl. 19, 197–203 (1967).
4. V. S. Vladimirov, ‘‘An approximate solution of a boundary value problem for a second-order differential equation,’’ Prikl. Mat. Mekh. 19, 315–324 (1955).
5. I. C. Gohberg and M. C. Krein, Theory and Applications of Volterra Operators in Hilbert Space, Translatations of Mathematical Monographs, Vol. 24 (American Mathematical Society, 1970).https://doi.org/10.1090/mmono/024