@misc{indiciae448b0ef7822a,
  title = {Covariant time-ordered perturbation theory.},
  author = {MG Fuda},
  year = {1986},
  doi = {10.1103/physrevc.33.996},
  url = {https://pubmed.ncbi.nlm.nih.gov/9953231/},
  note = {Source identifier: 9953231}
}