GHAZARYAN, H. Addition of lower order terms preserving almost hypoellipticity of polynomials. Eurasian Mathematical Journal, [S. l.], v. 4, n. 3, p. 32–52, 2013. Disponível em: https://emj.enu.kz/index.php/main/article/view/535. Acesso em: 5 aug. 2025.