ZHDANOV, R. Z.; TSIFRA, I. M. Reduction of differential equations and conditional symmetry. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 48, n. 5, p. 595–602, 1996. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5292. Acesso em: 5 dec. 2025.