KONEVA, N. P. Normal congruences with focal bicylindrical surfaces. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 45, n. 5, p. 718–720, 1993. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5859. Acesso em: 11 apr. 2025.