@misc{indiciaebb94787d075c,
  title = {Completely Integrable Differential Equations in Abstract Spaces.},
  author = {A D Michal and V Elconin},
  year = {1935},
  doi = {10.1073/pnas.21.9.534},
  url = {https://pubmed.ncbi.nlm.nih.gov/16577684/},
  note = {Source identifier: 16577684}
}