Shibata, T. „Variational Eigencurve and Bifurcation for Two-Parameter Nonlinear Sturm-Liouville Equations”. Topological Methods in Nonlinear Analysis, t. 8, nr 1, wrzesień 1996, s. 79-93, https://apcz.umk.pl/TMNA/article/view/TMNA.1996.022.