KLUN, Giuliano and SFECCI, Andrea. Well-ordered and non-well-ordered lower and upper solutions for periodic 2N-dimensional systems. Topological Methods in Nonlinear Analysis. Online. 8 March 2025. Vol. 65, no. 1, pp. 177 - 202. [Accessed 16 December 2025]. DOI 10.12775/TMNA.2024.026.