Andres, Jan, and Lech Górniewicz. “From the Schauder Fixed-Point Theorem to the Applied Multivalued Nielsen Theory”. Topological Methods in Nonlinear Analysis 14, no. 2 (December 1, 1999): 229–238. Accessed January 26, 2022. https://apcz.umk.pl/TMNA/article/view/TMNA.1999.030.