Andres, J., and L. Górniewicz. “From the Schauder Fixed-Point Theorem to the Applied Multivalued Nielsen Theory”. Topological Methods in Nonlinear Analysis, vol. 14, no. 2, Dec. 1999, pp. 229-38, https://apcz.umk.pl/TMNA/article/view/TMNA.1999.030.