VAIDZELEVICH, Aliaksei S. On spectra of upper Sergeev frequencies of linear differential equations. Journal of the Belarusian State University. Mathematics and Informatics, [S. l.], n. 1, p. 28–32, 2019. DOI: 10.33581/2520-6508-2019-1-28-32. Disponível em: https://journals.bsu.by/index.php/mathematics/article/view/926. Acesso em: 8 oct. 2026.