CHLEBICKA, Iwona, KARPPINEN, Arttu and LI, Ying. A direct proof of existence of weak solutions to elliptic problems. Topological Methods in Nonlinear Analysis. Online. 31 December 2023. Vol. 62, no. 2, pp. 643 - 665. [Accessed 22 July 2024]. DOI 10.12775/TMNA.2023.019.