NAGY, K. Approximation by Norlund means of quadratical partial sums of double Walsh - Kaczmarz - Fourier series. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 68, n. 1, p. 87–105, 2016. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/1824. Acesso em: 5 dec. 2025.