Apreutesei, Narcisia C., and Vitaly A. Volpert. “Properness and Topological Degree for Nonlocal Integro-Differential Systems”. Topological Methods in Nonlinear Analysis 43, no. 1 (April 12, 2016): 215–229. Accessed April 19, 2024. https://apcz.umk.pl/TMNA/article/view/TMNA.2014.012.