@misc{indiciaeadd924ca2c7e,
  title = {4-Dimensional Special Orthonormal Frames for Vacuum Gravity},
  author = {Estabrook, F. B. and Robinson, R. S. and Wahlquist, H. D.},
  year = {1996},
  url = {https://ntrs.nasa.gov/citations/20060036779},
  note = {Source identifier: 20060036779}
}