@misc{indiciae5def59438c5c,
  title = {ON THE BASIC APPROXIMATION THEOREM FOR SEMIGROUPS OF LINEAR OPERATORS.},
  author = {C Foias and G Gussi and V Poenaru},
  year = {1957},
  doi = {10.1073/pnas.43.7.616},
  url = {https://pubmed.ncbi.nlm.nih.gov/16590065/},
  note = {Source identifier: 16590065}
}