HUANG, L.; YU, J. ON THE EXISTENCE OF PERIODIC SOLUTIONS FOR A CLASS OF NONLINEAR DIFFERENTIAL SYSTEMS. Tamkang Journal of Mathematics, [S. l.], v. 24, n. 2, p. 173–188, 1993. DOI: 10.5556/j.tkjm.24.1993.4487. Disponível em: https://journals.math.tku.edu.tw/index.php/TKJM/article/view/4487. Acesso em: 3 may. 2024.