OLEINIK, E. V. On the Integration of a Nonlinear System of Differential Equations. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 66, n. 9, p. 1223–1234, 2014. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/2213. Acesso em: 5 dec. 2025.