PICHUGOV, S. A. Approximation of measurable periodic functions in measure by step functions. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 48, n. 5, p. 711–715, 1996. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5305. Acesso em: 6 dec. 2025.