@misc{indiciae8e64698d9d2e,
  title = {Small denominators, frequency operators, and Lie transforms for nearly integrable quantum spin systems.},
  author = {T Gramespacher and S Weigert},
  year = {1996},
  doi = {10.1103/physreva.53.2971},
  url = {https://pubmed.ncbi.nlm.nih.gov/9913233/},
  note = {Source identifier: 9913233}
}