YONGGANG; LI. On biharmonic surfaces in pseudo-Riemannian 4-dimensional space forms. Italian Journal of Pure and Applied Mathematics, [S. l.], v. 53, p. 294–304, 2025. Disponível em: https://journals.uniurb.it/index.php/ijpam/article/view/5653. Acesso em: 24 apr. 2026.