@misc{indiciae1888800c1dac,
  title = {Variational principle for time-dependent interactions.},
  author = {SJ Ward and JH Macek},
  year = {1991},
  doi = {10.1103/physreva.43.155},
  url = {https://pubmed.ncbi.nlm.nih.gov/9904766/},
  note = {Source identifier: 9904766}
}