Li, Shujie, and Jiabao Su. “Existence of Multiple Solutions of a Two-Point Boundary Value Problem at Resonance”. Topological Methods in Nonlinear Analysis 10, no. 1 (September 1, 1997): 123–135. Accessed July 22, 2024. https://apcz.umk.pl/TMNA/article/view/TMNA.1997.025.