@misc{indiciaeb12ec2de2d9b,
  title = {Singular integrals related to the Radon transform and boundary value problems.},
  author = {D H Phong and E M Stein},
  year = {1983},
  doi = {10.1073/pnas.80.24.7697},
  url = {https://pubmed.ncbi.nlm.nih.gov/16593402/},
  note = {Source identifier: 16593402}
}