On General Properties of Degenerate Systems of Second Order Partial Differential Equations of Hypergeometric Type. European Journal of Pure and Applied Mathematics, Maryland, USA, v. 14, n. 3, p. 1024–1043, 2021. DOI: 10.29020/nybg.ejpam.v14i3.4016. Disponível em: https://www.ejpam.com/index.php/ejpam/article/view/4016. Acesso em: 22 dec. 2024.