@misc{W3003660263,
  author = {А. Н. Тихонов and A. A. Samarskiĭ and Peter B. Kahn},
  title = {Equations of Mathematical Physics},
  year = {1965},
  howpublished = {American Journal of Physics},
  doi = {https://doi.org/10.1119/1.1971985}
}