Domingos, Ana Rute, i Miguel Ramos. „On the Solvability of a Resonant Elliptic Equation With Asymmetric Nonlinearity”. Topological Methods in Nonlinear Analysis, t. 11, nr 1, marzec 1998, s. 45-57, https://apcz.umk.pl/TMNA/article/view/TMNA.1998.003.