CHUNIKHIN, S. A. On extension of indexials. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 23, n. 5, p. 672–677, 1971. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/8339. Acesso em: 6 dec. 2025.