SIMEONOV , P. S., and D. D. BAINOV. “APPLICATION OF THE METHOD OF THE TWO-SIDED APPROXIMATIONS TO THE SOLUTION OF THE PERIODIC PROBLEM FOR IMPULSIVE DIFFERENTIAL EQUATIONS”. Tamkang Journal of Mathematics 22, no. 3 (September 1, 1991): 275–284. Accessed May 6, 2024. https://journals.math.tku.edu.tw/index.php/TKJM/article/view/4612.