1. Il’in, A. M. Matching of Asymptotic Expansions of Solutions of Boundary-Value Problems (Nauka, Moscow, 1989) [in Russian].
2. Il’in, A. M., Danilin, A. R. Asymptotic Methods in Analysis (Fizmatlit, Moscow, 2009) [in Russian].
3. Alymkulov, K. “Method of Boundary Layer Function to Solve the Boundary Value Problem for a Singularly Perturbed Differential Equation of the Order Two with a Turning Point”, Universal J. Appl. Math. 2, No. 3, 119–124 (2014).
4. Alymkulov, K., Asylbekov, T. D., and Dolbeeva, S. F. “Generalization of the Boundary Function Method for Solving Boundary-Value Problems for Bisingularly Perturbed Second-Order Differential Equations”, Math. Notes 94, No. 4, 451–454 (2013).
5. Alymkulov, K. and Khalmatov, A. A. “A Boundary Function Method for Solving theModel Lighthill Equation with a Regular Singular Point”, Math.Notes 92, No. 6, 751–755 (2012).