RAMESAN, Sithara; RAVINDRAN, K.T. Some results on K-frames. Italian Journal of Pure and Applied Mathematics, [S. l.], v. 43, p. 583–589, 2020. Disponível em: https://journals.uniurb.it/index.php/ijpam/article/view/7316. Acesso em: 6 nov. 2026.