@misc{indiciae93ad5a026164,
  title = {An Oscillation Theorem for Continuous Spectra.},
  author = {P Hartman and A Wintner},
  year = {1947},
  doi = {10.1073/pnas.33.12.376},
  url = {https://pubmed.ncbi.nlm.nih.gov/16588770/},
  note = {Source identifier: 16588770}
}