Agarwal, R. P. and O’Regan, D. (2003) “An essential map theory for ${\mathcal U}_c^{\kappa}$ and PK maps”, Topological Methods in Nonlinear Analysis, 21(2), pp. 375–386. Available at: https://apcz.umk.pl/TMNA/article/view/TMNA.2003.023 (Accessed: 3 March 2024).