Boliliy V. О.; Zelenska І. О. Non-stable differential turning point of the 2-nd kind for the fourth order system. Cherkasy University Bulletin: Physical and Mathematical Sciences, [S. l.], v. 389, n. 1, 2017. Disponível em: https://phys-ejournal.cdu.edu.ua/article/view/1379. Acesso em: 15 jun. 2026.