Stepanov, Eugene. “On Solvability of Some Boundary Value Problems for Differential Equations With ‘maxima’”. Topological Methods in Nonlinear Analysis 8, no. 2 (December 1, 1996): 315–326. Accessed April 19, 2024. https://apcz.umk.pl/TMNA/article/view/TMNA.1996.035.