1. Shkil’, N.I., Asimptoticheskie metody v differentsial’nykh
uravneniyakh (Asymptotic Methods in Differential Equations), Kiev: Vyshcha
Shkola, 1971.
2. Feshchenko, S.F., Shkil’, N.I., and Nikolenko, L.D., Asimptoticheskie
metody v teorii lineinykh differentsial’nykh uravnenii (Asymptotic Methods in the
Theory of Linear Differential Equations), Kiev: Naukova Dumka, 1966.
3. Daletskii, Yu.L., An asymptotic method for some differential equations with
oscillating coefficients, Dokl. Akad. Nauk SSSR, 1962,
vol. 143, no. 5, pp. 1026–1029.
4. Lomov, S.A., Vvedenie v obshchuyu teoriyu singulyarnykh
vozmushchenii (Introduction to the General Singular Perturbation Theory), Moscow:
Nauka, 1981.
5. Lomov, S.A. and Lomov, I.S., Osnovy matematicheskoi teorii
pogranichnogo sloya (Fundamentals of the Mathematical Theory of the Boundary
Layer), Moscow: Izd. Mosk. Gos. Univ., 2011.