KOSTIN, A. V. Problem of shadow in the Lobachevski space. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 70, n. 11, p. 1525–1532, 2018. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/1656. Acesso em: 5 dec. 2025.