,. In memory of I. M. Tsitelov (1936–2015). Vestnik of Saint Petersburg University. Mathematics. Mechanics. Astronomy, [S. l.], v. 3, n. 2, 2020. DOI: 10.21638/11701/spbu01.2016.221. Disponível em: https://math-mech-astr-journal.spbu.ru/article/view/9379. Acesso em: 17 may. 2024.