@misc{indiciae2eeeb4aa0f8b,
  title = {On barriers in a problem of collision avoidance},
  author = {Cliff, E. M. and Grantham, W. J. and Vincent, T. L.},
  year = {1971},
  url = {https://ntrs.nasa.gov/citations/19710040625},
  note = {Source identifier: 19710040625}
}