@misc{indiciaef1c9402f6954,
  title = {A First Approximation to Homotopy Theory.},
  author = {E H Spanier and J H Whitehead},
  year = {1953},
  doi = {10.1073/pnas.39.7.655},
  url = {https://pubmed.ncbi.nlm.nih.gov/16589320/},
  note = {Source identifier: 16589320}
}