GÓRNIEWICZ, Lech; NISTRI, Paolo. Topological essentiality and nonlinear boundary value control problems$^*$. Topological Methods in Nonlinear Analysis, [S. l.], v. 13, n. 1, p. 53–72, 1999. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.1999.003. Acesso em: 8 jul. 2025.