@misc{indiciae36a299d7c51f,
  title = {SOME FUNCTION CLASSES CONNECTED WITH PARTIALLY HYPOELLIPTIC DIFFERENTIAL OPERATORS.},
  author = {J Friberg},
  year = {1962},
  doi = {10.1073/pnas.48.1.22-b},
  url = {https://pubmed.ncbi.nlm.nih.gov/16590912/},
  note = {Source identifier: 16590912}
}