@misc{indiciaea8b412dd2f15,
  title = {An Ergodic Theorem for General Semi-Groups.},
  author = {G Birkhoff},
  year = {1939},
  doi = {10.1073/pnas.25.12.625},
  url = {https://pubmed.ncbi.nlm.nih.gov/16588310/},
  note = {Source identifier: 16588310}
}