ELABBASY, E. M. SINGULAR PERTURBATIONS FOR THE FORCED VAN DER POL OSCILLATOR. Tamkang Journal of Mathematics, [S. l.], v. 24, n. 4, p. 417–430, 1993. DOI: 10.5556/j.tkjm.24.1993.4514. Disponível em: https://journals.math.tku.edu.tw/index.php/TKJM/article/view/4514. Acesso em: 23 apr. 2024.