SHAHZAD, N. On $ R $-subcommuting maps and best approximations in Banach spaces. Tamkang Journal of Mathematics, [S. l.], v. 32, n. 1, p. 51–53, 2001. DOI: 10.5556/j.tkjm.32.2001.368. Disponível em: https://journals.math.tku.edu.tw/index.php/TKJM/article/view/368. Acesso em: 2 may. 2024.