Caponetti, Diana, Alessandro Trombetta, and Giulio Trombetta. “Proper $k$-Ball-Contractive Mappings in $C_b^m[0, + \infty)$”. Topological Methods in Nonlinear Analysis 58, no. 2 (December 13, 2021): 609–639. Accessed June 29, 2025. https://apcz.umk.pl/TMNA/article/view/36494.