VALENCIA, Fabricio. Notes on flat pseudo-Riemannian manifolds. Pro Mathematica, [S. l.], v. 30, n. 60, p. 11–50, 2019. Disponível em: https://revistas.pucp.edu.pe/index.php/promathematica/article/view/21091. Acesso em: 12 dic. 2025.