Hu, S. and Papageorgiou, N. S. (2009) “Nontrivial solutions for superquadratic nonautonomous periodic systems”, Topological Methods in Nonlinear Analysis, 34(2), pp. 327–338. Available at: https://apcz.umk.pl/TMNA/article/view/TMNA.2009.045 (Accessed: 20 April 2024).