ANDRIENKO, V. A. On the almost-everywhere convergence of the Riesz means of double orthogonal series. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 51, n. 7, p. 867–880, 1999. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4676. Acesso em: 5 dec. 2025.