@misc{indiciae563471ba7de1,
  title = {Dynamical Systems of Continuous Spectra.},
  author = {B O Koopman and J V Neumann},
  year = {1932},
  doi = {10.1073/pnas.18.3.255},
  url = {https://pubmed.ncbi.nlm.nih.gov/16587673/},
  note = {Source identifier: 16587673}
}