ZELINSKII, Yu. B.; STEFANCHUK, M. V. Generalizations of the shadow problem. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 68, n. 6, p. 757–763, 2016. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/1876. Acesso em: 14 apr. 2025.