BARTOLO, R.; GERMINARIO, A.; SANCHEZ, M. Orthogonal trajectories on stationary spacetimes under intrinsic assumptions. Topological Methods in Nonlinear Analysis, [S. l.], v. 24, n. 2, p. 239–268, 2004. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2004.027. Acesso em: 22 lip. 2024.