Gliklikh, Yuri E. “Total and Local Topological Indices for Maps of Hilbert and Banach Manifolds”. Topological Methods in Nonlinear Analysis 15, no. 1 (March 1, 2000): 17–31. Accessed April 26, 2024. https://apcz.umk.pl/TMNA/article/view/TMNA.2000.002.