Klun, Giuliano, and Andrea Sfecci. “Well-Ordered and Non-Well-Ordered Lower and Upper Solutions for Periodic 2N-Dimensional Systems”. Topological Methods in Nonlinear Analysis 65, no. 1 (March 8, 2025): 177–202. Accessed June 28, 2025. https://apcz.umk.pl/TMNA/article/view/59306.