DMITRIENKO, V. T.; ZVYAGIN, V. G. Index of solution set for perturbed Fredholm equations and existence of periodic solutions for delay differential equations. Topological Methods in Nonlinear Analysis, [S. l.], v. 21, n. 1, p. 53–80, 2003. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2003.004. Acesso em: 22 jul. 2024.