Bartolo, Rossella, Anna Germinario, and Miguel Sanchez. “Orthogonal Trajectories on Stationary Spacetimes under Intrinsic Assumptions”. Topological Methods in Nonlinear Analysis 24, no. 2 (December 1, 2004): 239–268. Accessed July 3, 2024. https://apcz.umk.pl/TMNA/article/view/TMNA.2004.027.