VOULOV, H. D.; BOHNER, M. J.; BEKKER, M. B. A q-difference operator with discrete and simple spectrum. Methods of Functional Analysis and Topology, [S. l.], v. 17, n. 4, p. 281–294, 2011. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/493. Acesso em: 16 dec. 2025.