@misc{indiciaed4a054c7c722,
  title = {Abstract Critical Sets.},
  author = {M Morse and G B Van Schaack},
  year = {1935},
  doi = {10.1073/pnas.21.5.258},
  url = {https://pubmed.ncbi.nlm.nih.gov/16577667/},
  note = {Source identifier: 16577667}
}