@misc{indiciae4a137b0d7e84,
  title = {Degenerate gravitational fields with twisting rays.},
  author = {Robinson, I. and Robinson, J. R. and Zund, J. D.},
  year = {1969},
  url = {https://ntrs.nasa.gov/citations/19690054843},
  note = {Source identifier: 19690054843}
}