Amster P, De Nápoli P. On a generalization of Lazer-Leach conditions for a system of second order ODE’s. TMNA [Internet]. 2009 Mar. 1 [cited 2024 Jul. 3];33(1):31-9. Available from: https://apcz.umk.pl/TMNA/article/view/TMNA.2009.003