GUBREEV , G. M.; IGNATENKO , T. R. On the class of orthogonalizators of the families of exponents with real frequencies. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 44, n. 8, p. 1031–1044, 1992. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/8031. Acesso em: 5 dec. 2025.