The Exterior Tricomi and Frankl Problems for Quaterelliptic-Quaterhyperbolic Equations with Eight Parabolic Lines. European Journal of Pure and Applied Mathematics, Maryland, USA, v. 4, n. 2, p. 186–208, 2011. Disponível em: https://www.ejpam.com/ejpam/article/view/1175. Acesso em: 24 feb. 2026.