@article{Perrot78,
  title = {Varietes de Langages et Operations},
  author = {Jean-François Perrot},
  year = {1978},
  researchr = {https://researchr.org/publication/Perrot78},
  cites = {0},
  citedby = {0},
  journal = {Theoretical Computer Science},
  volume = {7},
  pages = {197-210},
}