@misc{indiciae25b793e9271b,
  title = {Unstable periodic orbits in the parametrically excited pendulum.},
  author = {van de Water W and M Hoppenbrouwers and F Christiansen},
  year = {1991},
  doi = {10.1103/physreva.44.6388},
  url = {https://pubmed.ncbi.nlm.nih.gov/9905769/},
  note = {Source identifier: 9905769}
}