O’Regan, Donal. „Upper and Lower Solutions for Problems With Singular Sign Changing Nonlinearities and With Nonlinear Boundary Data”. Topological Methods in Nonlinear Analysis 19, no. 2 (czerwiec 1, 2002): 375–390. Udostępniono lipiec 22, 2024. https://apcz.umk.pl/TMNA/article/view/TMNA.2002.019.