@misc{indiciaeb2b215a7f7a8,
  title = {Modular group, operator ordering, and time in (2+1)-dimensional gravity.},
  author = {S Carlip},
  year = {1993},
  doi = {10.1103/physrevd.47.4520},
  url = {https://pubmed.ncbi.nlm.nih.gov/10015451/},
  note = {Source identifier: 10015451}
}