@misc{indiciae31c850994940,
  title = {A Simple Second Order Differential Equation with Singular Motions.},
  author = {N Levinson},
  year = {1948},
  doi = {10.1073/pnas.34.1.13},
  url = {https://pubmed.ncbi.nlm.nih.gov/16588775/},
  note = {Source identifier: 16588775}
}