Ďurikovič, Vladimír, and Monika Ďurikovičová. “Sets of Solutions of Nonlinear Initial-Boundary Value Problems”. Topological Methods in Nonlinear Analysis 17, no. 1 (March 1, 2001): 157–182. Accessed April 16, 2024. https://apcz.umk.pl/TMNA/article/view/TMNA.2001.011.