@misc{indiciaec07ff3858d7f,
  title = {A UNIFYING PRINCIPAL IN QUANTIFICATION THEORY.},
  author = {R M Smullyan},
  year = {1963},
  doi = {10.1073/pnas.49.6.828},
  url = {https://pubmed.ncbi.nlm.nih.gov/16591106/},
  note = {Source identifier: 16591106}
}