Capietto, Anna, Jean Mawhin, and Fabio Zanolin. 1995. “On the Existence of Two Solutions With a Prescribed Number of Zeros for a Superlinear Two-Point Boundary Value Problem”. Topological Methods in Nonlinear Analysis 6 (1):175-88. https://apcz.umk.pl/TMNA/article/view/TMNA.1995.039.