Botyuk, A. O. “Quasilinear Periodic Boundary-Value Problem”. Ukrains’kyi Matematychnyi Zhurnal 49, no. 12 (December 25, 1997): 1690–1693. Accessed May 19, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/5174.