CHERNIKOV, S. N. Om Shmidt’s problem. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 23, n. 5, p. 598–603, 1971. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/8332. Acesso em: 6 dec. 2025.