1. K. Alymkulov and D. A. Tursunov, “On a method of construction of asymptotic decompositions of bisingular perturbed problems,” Izv. Vyssh. Uchebn. Zaved., Mat., No. 12, 3–11 (2016).
2. K. Alymkulov and A. A. Khalmatov, “A boundary function method for solving the model Lighthill equation with a regular singular point,” Math. Notes 92, 751–755 (2012).
3. K. Alymkulov, T. D. Asylbekov, and S. F. Dolbeeva, “Generalization of the boundary function method for solving boundary-value problems for bisingularly perturbed second-order differential equations,” Math. Notes 94, 451–454 (2013).
4. J. D. Cole, Perturbation Methods in Appled Mathematics (Blaisdell, Waltham, MA, 1968).
5. V. Ekhaus, Matched Asymptotic Expansions and Singular Perturbation (North-Holland, Amsterdam, 1973).