VIZEL, Ya. On some generalization of Favard theorem for multidimensional case. Lithuanian Mathematical Journal, [S. l.], v. 10, n. 1, p. 13–15, 1970. DOI: 10.15388/LMJ.1970.20832. Disponível em: https://www.zurnalai.vu.lt/LMJ/article/view/20832. Acesso em: 28 apr. 2025.