ROH, E. H.; JUN, Y. B.; KIM, S. Y.; SHIM, W. H. On properties of nil subsets in difference algebras. Tamkang Journal of Mathematics, [S. l.], v. 32, n. 3, p. 167–172, 2001. DOI: 10.5556/j.tkjm.32.2001.371. Disponível em: https://journals.math.tku.edu.tw/index.php/TKJM/article/view/371. Acesso em: 2 may. 2024.