@misc{indiciae2d65ca3da2ed,
  title = {Introductory concepts},
  author = {Childs, J. H. and Cortright, E. M. and Gabriel, D. S. and Wyatt, D. M. D.},
  year = {1957},
  url = {https://ntrs.nasa.gov/citations/19710070019},
  note = {Source identifier: 19710070019}
}