PAVLENKO , V. A. Periodical orgraphs and their properties. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 40, n. 4, p. 528–532, 1988. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/9194. Acesso em: 6 dec. 2025.