CHAOHA, Phichet; GOEBEL, Kazimierz; TERMWUTTIPONG, Imchit. Around Ulam’s question on retractions. Topological Methods in Nonlinear Analysis, [S. l.], v. 40, n. 1, p. 215–224, 2012. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2012.029. Acesso em: 8 jul. 2025.