AN, M.-Q. A note on an open problem. Tamkang Journal of Mathematics, [S. l.], v. 43, n. 2, p. 281–287, 2012. DOI: 10.5556/j.tkjm.43.2012.1184. Disponível em: https://journals.math.tku.edu.tw/index.php/TKJM/article/view/1184. Acesso em: 29 apr. 2024.