Ize, Jorge, and Alfonso Vignoli. “Equivariant Degree for Abelian Actions. Part III: Orthogonal Maps”. Topological Methods in Nonlinear Analysis 13, no. 1 (March 1, 1999): 105–146. Accessed July 22, 2024. https://apcz.umk.pl/TMNA/article/view/TMNA.1999.006.