AGARWAL, R. P.; O’REGAN, D. An essential map theory for ${\mathcal U}_c^{\kappa}$ and PK maps. Topological Methods in Nonlinear Analysis, [S. l.], v. 21, n. 2, p. 375–386, 2003. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2003.023. Acesso em: 25 feb. 2024.