@misc{indiciae37615965a142,
  title = {Normal ordering for continuum fields by functional differentiation.},
  author = {SM Barnett},
  year = {1991},
  doi = {10.1103/physreva.43.6418},
  url = {https://pubmed.ncbi.nlm.nih.gov/9904983/},
  note = {Source identifier: 9904983}
}