ALEKSANDROVICH, I. N. Differential operators determining solutions of Elliptic equations. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 47, n. 12, p. 1587–1592, 1995. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5552. Acesso em: 5 dec. 2025.