HASENAUER, R. E.; KUBIK, B. $\tau$-Atomicity and Quotients of Size Four. Tamkang Journal of Mathematics, [S. l.], v. 52, n. 2, p. 221-228, 2021. DOI: 10.5556/j.tkjm.52.2021.3241. Disponível em: https://journals.math.tku.edu.tw/index.php/TKJM/article/view/3241. Acesso em: 24 jun. 2021.