Bartsch, T., i T. Weth. „The Effect of the domain’s Configuration Space on the Number of Nodal Solutions of Singularly Perturbed Elliptic Equations”. Topological Methods in Nonlinear Analysis, t. 26, nr 1, wrzesień 2005, s. 109-33, https://apcz.umk.pl/TMNA/article/view/TMNA.2005.027.