,. On anniversary of S.B. Filippov. Vestnik of Saint Petersburg University. Mathematics. Mechanics. Astronomy, [S. l.], v. 4, n. 1, p. 174–175, 2020. Disponível em: https://math-mech-astr-journal.spbu.ru/article/view/8589. Acesso em: 18 may. 2024.