@misc{indiciaeab01751f9f4c,
  title = {Invariant imbedding and perturbation techniques applied to diffuse reflection from spherical shells},
  author = {Bellman, R. E. and Kagiwada, H. H. and Kalaba, R. E.},
  year = {1965},
  url = {https://ntrs.nasa.gov/citations/19650024263},
  note = {Source identifier: 19650024263}
}