Konisbayeva, K. T., M. K. Dauylbayev, and N. R. Tortbay. “INTEGRAL BVP FOR SINGULARLY PERTURBED SYSTEM OF DIFFERENTIAL EQUATIONS”. International Journal of Mathematics and Physics, vol. 12, no. 1, Sept. 2021, pp. 25-33, doi:10.26577/ijmph.2021.v12.i1.04.