Dondè T, Zanolin F. Multiple periodic solutions for one-sided sublinear systems: A refinement of the Poincaré-Birkhoff approach. TMNA [Internet]. 2020 May 31 [cited 2024 Apr. 23];55(2):565-81. Available from: https://apcz.umk.pl/TMNA/article/view/TMNA.2019.104