MAHER, Philip J.; SAL MOSLEHIAN, Mohammad. More on approximate operators. CUBO, A Mathematical Journal, [S. l.], v. 14, n. 1, p. 111–117, 2012. DOI: 10.4067/S0719-06462012000100009. Disponível em: https://cubo.ufro.cl/index.php/cubo/article/view/1357. Acesso em: 12 oct. 2025.