CHOUDHRY, R. K. Transformation of Birkhoff’s Rings into themselves and Rotational Numbers. The Journal of the Indian Mathematical Society, [S. l.], v. 30, n. 1, p. 27–45, 1966. DOI: 10.18311/jims/1966/16799. Disponível em: http://informaticsjournals.com/index.php/jims/article/view/16799. Acesso em: 4 may. 2024.